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Author Topic:   Doel-Fin--Five Years of Opinions
Steve Whichello posted 04-19-2001 11:38 PM ET (US)   Profile for Steve Whichello   Send Email to Steve Whichello  
I have purchased a [Davis-brand anti-ventilation plate appendage called a] Doel-Fin to be installed on my 1990 Yamaha Montauk rig, This came about after having made the decision to install a rear seat. I figured even with my pork belly brother in law for a ride I should have better planing control with the added weight of rear passengers. Any final remarks before I "Cringe" and drill holes in my cavitation plate!.
B Bear posted 04-20-2001 12:32 AM ET (US)     Profile for B Bear  Send Email to B Bear     
Steve I have some Doel-Fins sitting in the basement waiting for that fateful day. Please let me know how yours work out.
whalertim posted 04-20-2001 07:43 AM ET (US)     Profile for whalertim  Send Email to whalertim     
I am waiting for the same! I installed a sternseat on my Montauk this past winter. Took the boat out last weekend to Surf City to do a little boating. The water at low tide this time of year is really low. I thought that a fin might make a difference. Let me know how it goes.
Dick posted 04-20-2001 08:55 AM ET (US)     Profile for Dick  Send Email to Dick     
I too have a Doel-Fin awaiting installation.
I am going to drill the holes then go to the lake and make a run paying attention to the performance, then go back to the ramp, bolt it on and repeat.
I want to know the performance difference under the same conditions.

Once said I would never install one but feedback here has convinved me to give it a try.

Ventura16 posted 04-20-2001 10:10 AM ET (US)     Profile for Ventura16  Send Email to Ventura16     
That's a coincidence! I just bought one last weekend at Bass Pro Shops. I'm just waiting for the weather to improve so I can go out and start drilling...maybe this weekend. I never would have seriously considered it without the input from folks on this forum...what a great resource you all are!


1961bugeye posted 04-20-2001 10:45 AM ET (US)     Profile for 1961bugeye  Send Email to 1961bugeye     
I am also considering a Doel-Fin. My 1987 Montauk 110hp Johnson seems to need a lot of speed to get it on plane. What do the manufacturers say about Doel-Fins? If they are so great why doesn't the motor have a wider plate?
Chris J posted 04-20-2001 11:45 AM ET (US)     Profile for Chris J  Send Email to Chris J     
Last year, I installed fins on my 150 Evinrude, driving a Revenge 20. I can't say as they made a whole lot of difference. Maybe a little faster getting up on plane.

If you really need to push the bow down, trim tabs are probably the way to go. They actually push on the hull, rather than pushing up on the drive to push up on the hull.

I'm not sure why motor mfgs. put such puny cavitation plates on their motors though. Probably saves some money.

triblet posted 04-20-2001 12:08 PM ET (US)     Profile for triblet  Send Email to triblet     
A Doel-Fin catches kelp like crazy, which is
one reason I don't have one. The other
reason is that I also don't understand why
the motor manufacturers don't include one.
There's gotta be a reason. Maybe it's that
they don't make sense on a non-planing hull.


Barry posted 04-20-2001 12:27 PM ET (US)     Profile for Barry  Send Email to Barry     
Chris J, what brand of fin did you use?

I also recently purchased a Doel-Fin at BassPro for the Mercury 90 on my Montauk. I'm hoping that it will keep the boat on plane at lower speeds.

JimU posted 04-20-2001 01:52 PM ET (US)     Profile for JimU  Send Email to JimU     
Does anyone know how using one affects motor warranty? JIM
awares posted 04-20-2001 03:48 PM ET (US)     Profile for awares  Send Email to awares     
Before you drill any holes have you considered that you might not have the right prop.

The boat will only perform as good as the prop. I would talk to a prop professional and explain to them on what you are trying to accomplish first.

I want a quick hole shot with a minimum amount of things in the water to catch on.

Match the motor with the correct prop so you have maximized the motors performance. If you are still not happy consider other options. Motor height, set back plate, tabs and fins.

If you want someone to talk to about props call Nettle's Prop Shop at 1-800-517-7707 or email them at

They are great and they know what they are talking about.

Allen Wares

daverdla posted 04-20-2001 03:48 PM ET (US)     Profile for daverdla  Send Email to daverdla     
Just took my 1989 Montauk out for the first time (second try). It has a 1992 Evinrude 100 with Doel-Fins. One fin is cracked. Both fins are warped. At full throttle the boat leans to port. Looking at the way the fins are warped, this would make sense. I'm wondering if I should replace the fins or just get rid of them. Is warping a commong problem? Has anyone else seen warped fins? What would cause them to warp?
Chris J posted 04-20-2001 06:47 PM ET (US)     Profile for Chris J  Send Email to Chris J     
My fins aren't actually Doel-Fins, but very similar. Can't remember the make right offhand. There are 2 fins in the set. Each is slightly narrower than a Doel-Fin.
DIVE 1 posted 04-20-2001 09:24 PM ET (US)     Profile for DIVE 1    
We have had Doel-Fins on DIVE 1 for four seasons now and we love them. When we first built the boat, the engines had to be at 4,000RPMs to stay on plane. Trim tabs were beyond our budget at the time but the Doel-Fins were donated. We installed them and went for a test run. The boat would plane at 2,500-RPM and our fuel consumption dropped considerably. Even with 6 people, 125-gals. of fuel and 1,000-lbs of dive gear the boat stays on plane at 2,800-RPM. I have installed these fins on numerous boats and have always seen a dramatic improvement in trim control and lower speeds to plane.
Sawgrass posted 04-20-2001 10:51 PM ET (US)     Profile for Sawgrass  Send Email to Sawgrass     
I have considered installing a Doel-Fin on my 15' Sport/70 HP OMC but have been attracted to the looks of a sleeker, more compact fin/stabilizer made by Bob's Machine Works. It appears to be aluminum and about half the size of a comparable Doel-Fin. Bob claims that it has all the perfomance of the broad tail fins. I know that Bob's makes some of the best jack plates and other high quality boating accessories but have not heard anything about their stabilizer. Anyone have any feedback about this produt?


jimh posted 04-21-2001 04:08 AM ET (US)     Profile for jimh  Send Email to jimh     
If you drill the holes, mount the Doel-Fin, and decide it doesn't work out, you can always repair the damage.



Clark Roberts posted 04-21-2001 04:47 AM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
Sawgrass, the Doel-Fin is a hydrofoil and provides lift (like an airplane wing) while also keeping a lid on the prop. You should be able to raise your engine a notch or two with the Doel-Fin (use the actual brand name and not some substitute like the "stingray", which is a hydrospoiler - has a turned down trailing edge and may help a stern heavy boat keep the bow down)! The Bob's Machine stabilizer is a fine piece of hardware but intended to stabilize hyper-fast bass boats etc, which have almost no hull in the water! The stabilizer has two small keels beneath which rudder the boat and provide steerage... I have experience with both and recommend the Doel-Fin wholeheartedly. Others may have had revealing experiences also.. Put the doe-fin on, raise the engine and don't look back! Happy Whalin'.. Clark.. The Old Man and the Sea
kingfish posted 04-21-2001 08:57 AM ET (US)     Profile for kingfish  Send Email to kingfish     
I'm with Clark...I started out with Doel-Fins on a 13' Zodiac I had with a 30-HP Yamaha that struggled to get and stay on plane at moderate RPM (it had plenty of hp, but there was too big a barrier to break through, so once you got on plane, you had just added 10 or more MPH to your speed, and you couldn't operate anywhere in that range of speed between plowing and planing), and it was an absolute wild thing at WOT. The Doel-Fin turned that rig right into a domesticated animal.

Had and appreciated the Doel-Fins on both my Montauks, and when I bought my 22' Outrage, I mounted them on the 225 Evinrude and was pleased with the results. Kept them on until I installed trim tabs...I strongly recommend them for these types of applications, though I imagine they are a problem in kelp-ridden areas, as Chuck has mentioned.

FISHNFF posted 04-21-2001 04:21 PM ET (US)     Profile for FISHNFF  Send Email to FISHNFF     
I have run Doel-Fins on my 13 and my 17 and have found good success with both. The boats plane at lower speeds and make a noticeable when loaded. My 13 I ran on the second hole up, which in itself made a difference. My 17, with a heavy Merc 90 4 stroke, is run on the third hole up. Trimmed properly there is very little bow rise and hole shot is good, though not sharp like a 2 stroke. Can plane at a comfortable speed to run through that 2' chop and those 4' rollers that a faster speed would launch you off of. I have not actually sat down and crunched the numbers, but they must help fuel economy. I ran a 17 and a 22 with a Stingray and thought them terrible. The 17 had an instant plane but hard to really get the boat up and out of the water for max speed. The 22 at anything less than neutral trim wanted to force the bow down and cause an annoying if not dangerous knifing/carving tendency which the boat would pitch and veer whichever way the bow was pointed. A friend had better success with a Stingray over a Doel-Fin, but that was on a 15 1/2' bassboat with an 80 Merc with livewell, batteries, and fuel in the stern. Really squatted.
ron miller posted 04-21-2001 09:30 PM ET (US)     Profile for ron miller  Send Email to ron miller     
just put on Doel-Fin on my 13 foot super, 1975, has a 40 horse Evinrude with rejetted carbs, dyno at 50 horsepower, I would diffently do it.
B Bear posted 04-22-2001 11:00 PM ET (US)     Profile for B Bear  Send Email to B Bear     
Clark (The Old Man and the Sea)
Whey is it important to raise the engine up one hole? Normally doesn't the cavitation plate line up with the bottom of the transom.
JimU posted 04-24-2001 10:32 AM ET (US)     Profile for JimU  Send Email to JimU     
Are there any warranty problems if you install a doelfin or other such device on a new engine? Jim
Dick posted 04-24-2001 08:21 PM ET (US)     Profile for Dick  Send Email to Dick     
I am sure the engine manufacturer is not going to warranty any problem caused by any aftermarket add on. The engine warranty basicly covers defects in material and workmanship and a Doel-Fin should have no bearing on that. I read my Mercury warranty and no where does it state that aftermarket add ons will void the warranty.

I have been in the marine parts business for over 30 years and have never heard of a problem to an engine caused by a Doel-Fin or any of the other imitations.


willyjoe1 posted 04-25-2001 10:51 PM ET (US)     Profile for willyjoe1  Send Email to willyjoe1     
What is the differance between Doel-Fin and a whale tail when i bought my 86 13'it mounted with that whaler tail on 28 spl. johnson it on plane fast with 1 or 2 peoples on board i feel sorry to sold the motor w/ that whaler tail when i repower it at 98, could any one know that differance between this 2 appreciate any though william
B Bear posted 04-30-2001 04:51 PM ET (US)     Profile for B Bear  Send Email to B Bear     
I just got off the phone with the Honda customer service engineering department. The Doel-Fin will not void the warranty on the engine or lower unit, but will void the warranty on the lower unit housing if damage should occur to the housing where the fin is attached.
Clark Roberts posted 05-01-2001 05:26 PM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
Bear, the higher you can run an engine and maintain cooling water flow, the better as there is less lower unit drag! Handling will be better as will economy and top speed. An advantage of a set-back bracket or jack-plate is that engine can be raised higher as it's running in cleaner (less bubbles and turbulance) water. Suggest that you raise engine a hole at a time until you get cavitation on take-off and /or in hard turn and then drop it back a notch.. keep an eye on the cooling "tattle tale" stream to ensure cooling water flow.. I remember in the old days (1960's) when I was running big in-line 6 cyl Mercs that I always used a water press gage and watched it constantly as the big mercs would raise a hull out of the water.. in those days we had distributors with points and condenser etc and elec systems were constant trouble.. not so these days! getting off the subject as usual... Clark
B Bear posted 05-01-2001 06:37 PM ET (US)     Profile for B Bear  Send Email to B Bear     
Thank you Clark.
Erik posted 05-01-2001 08:42 PM ET (US)     Profile for Erik    
I was thinking, if u raise your engine up a couple notches as described above, when u try to trim the engine up to get the bow up wouldnt the engine come out of the water and start to cavitate? That is my only worry i have about raising my engine. When runnin in rough choppy sea i always like to raise the bow enough so that the belly of the boat takes all the pounding rather than the hull.This way to me it feels alot better. Would i still be able to do this with a raised engine?
Clark Roberts posted 05-02-2001 08:05 AM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
Eric, I have never had a trim range problem with engine mounted up high! You may want to try it for yourself as you can always drop engine back down! You see, I can never let well enough alone and must alway "fiddle" with everything... guess I will always suffer from this malady (anyway I hope so).... Happy Whalin'.. Clark .. Spruce Creek Navy
OutrageMan posted 05-02-2001 02:23 PM ET (US)     Profile for OutrageMan  Send Email to OutrageMan     
Last season, I put a Stingray Hydrofoil on my 22 Outrage WD with a 250 V-x Yamaha. This boat suffered from extreme torque list at speed. The hydrofoil easily corredted this problem. It also allowed me to use the entire range of the trim.

This fin did take some getting used to though. Coming out of the pocket quickly drove the bow down very fast, and if I wast with it on the trim, created a situation that was just short of a "pitch-pull" (as a matter of facct, if I remember correctly it nearly threw my father "Harpoon Harry" into the bow from the console). After knowing what to expect now, there is no problem.

I have to say that this is definately the best $30 I have spent ton the boat.


B Bear posted 05-19-2001 01:42 PM ET (US)     Profile for B Bear  Send Email to B Bear     
I installed the Doel-Fin. Here is what happened:
I was able to get up on plane easier, this reduced a dead space in the rpm range where the hull wanted to get on plane but couldn't. I also had an increase in my effective trim range. I remained on plane longer, dropped off plane at 3500 rpm with fins and 4000 rpm without. I lost maybe 1 -2 mph off the top end and if I trimed up to get back the top end speed I need to trim down when making a high speed turn or I would bounce through it.
I have yet to raise the engine. I feel that the benefits out weigh the small loss on the top end speed.
whalernut posted 05-21-2001 05:13 PM ET (US)     Profile for whalernut  Send Email to whalernut     
I have the Stingray on my `16 Currituck with a 85h.p. Johnson. It gets me on plane in an instant, but the bow does push down a little to much. Does anyone know anything about the SE Sport 300 wing in the Overton`s magazine. It is medium sized with ribbz on the bottom for traction and 2 slight trailing edges? I like the size and style of this one, the price is $40 plus? My Brother uses the aluminum THE EDGE wing on his Sea Ray and loves what it has done for planing! He reccomends this one at $50? Regards-Jack Graner.
Whaletosh posted 05-22-2001 08:18 AM ET (US)     Profile for Whaletosh    

I have used the SE Sport 300 on 2 boats. The reason that I got the first one was because seceral years ago Trailer Boats magazine id a comparison of several of the "foils". The SE Sport 300 was the second fastest for planing, and was the one that had the least affect on top end speed. The difference between the planing speed was miniscule.

I tried the SE Sport 300 (got it from Cabelas) on my 13 Sport. The results were terrible. Slower to plane, porposing, lower top end. I just plugged the holes with MarineTek and all was fine.

I may try the SE Sprt 300 on my Dauntless 14, but only if I am dissappointed with the perfermance of the boat.


Dick posted 05-22-2001 09:41 AM ET (US)     Profile for Dick  Send Email to Dick     
I just installed a Doel-Fin and didn't notice any improvement but did loose a couple mph. 17 Montauk with Merc 50hp 4 stroke. Engine is mounted up 1 hole, think I will raise it one more and see what that does. Next time out I am going to run it both with and witout the Doel-Fin for comparison.
lpaton posted 05-24-2001 08:20 AM ET (US)     Profile for lpaton  Send Email to lpaton     
Got to try the Doel-Fin yesterday with full tank of gas and solo. Top speed now 45 mph vs 47 mph before. Will plane at 23 mph vs 30 mph before Faster to get on plane. I wiil keep it on and possibly raise engine a hole.
mattr posted 05-24-2001 08:43 AM ET (US)     Profile for mattr  Send Email to mattr     
I was on the Mercury website yesterday, and was casually reading the FAQ page, and there is a question about the addition of the Doel-Fins...they do mention that any damage that occurs from the use of these fins will void the warranty...don't remember which part of the engine will not be covered, but I assume that it refers to the lower unit coverage...
lhg posted 05-24-2001 08:52 PM ET (US)     Profile for lhg    
I guess another point of view is always of value on a site like this. There are a few points about these that interest me. It's clear they slow down most boats. Doesn't seem like a plus to me. It's also clear that that most report an improvement in lower planing speeds, presumeably from the stern lift these would provide as the hull comes out of the hole, with water pushing against the fin. My guess is that this results in increased drag, and loss of fuel efficiency as a trade off. With today's improved propeller technology, most engines 40HP and up, should be installed with the anti-cavitation plate running about 1/2" above the water surface coming off the planing hull bottom, so the only period of time when one of these things would have any effect at all is from 0-18mph, while achieving plane.

Another item of interest are the comments that one's Whaler needs 30mph to plane. Just has not been my experience with Whalers at all. Both my 18 & 25 Outrages will easily stay on plane at 20mph, with no fins or trim tabs. In both cases the engine RPM's are around 2200. Same for the 13' & 16' hulls.


1. As Triblet has pointed out, how could ALL of the engine manufacturers be so stupid as to not include such design as original equipment on their engines. Something is wrong with this picture.

2. Has anybody ever seen one of these on any type of performance go-fast, offshore performance, or high speed bass boat? I attended the Bass Masters Classic a year ago, and didn't see one Doel-Fin.

3. On larger boats, wouldn't trim tabs be a better solution for hull running attitude control?

Finally, let me be (only) a MESSENGER. About 7 years ago, Powerboat Reports, a fairly well respected Marine testing guide, did an exhaustive study and test of these various fins, and concluded they were totally worthless. They could find no reason to justify using them under any boating condition. They used various engine HP's and various boats, and concluded they hurt overall performance more than they helped.
I remember the article stated that most of the advertizing claims were false. They also contacted the engine companies, who also had tested them and found they added nothing to overall efficiency or engine performance. They basically said that "we'd add it to our cavitation plate design if we thought it helped."

Disclaimer: I should also say that because of this article, I have never bothered to try one of these out. So please consider my remarks in that light.

B Bear posted 05-24-2001 11:25 PM ET (US)     Profile for B Bear  Send Email to B Bear     
Counter Points:
There are quite a few things that have not been added to products that are beneificial some examples would be:
The air bags that are standard today were introduced in the 60's.
Steering skags for jet propelled craft to allow steerage when not under power.
How about a water seperator and fuel filter which are not standard for many outboards today.

Engine manufacturers are not stupid, they have no need to address the trim issue when there are trim tabs to do this for larger boats and fins for smaller boats.

Common sence is that anything you add on to the lower unit will increase drag and reduce top end. Common sence also tells you that if you can remain at plane longer and get on plane faster at less rpms that you have reduced hull drag and increased fuel efficency.

There are articles written that have compared fins (as in Trailer Boat Mag) and made recommendations as to which ones are best and there are articles wrtten that say these things are worthless.

This is from "SaltWater Sportsman" Vol 62, No 5. May 2001, the article: Improve Performance with Trim Tabs, page 24.
"lowered tabs create substantial lift to raise the stern faster, so you're off and running quicker. That is a big concern in small boats like falts skiffs in situations where you have to jump on plane in a short distance. Alternatively, bolt-on cavitation-plate extenions (wing-like devices that attach to your outboard's lower unit) provide some of the same lift that a full set of tabs does, but at a much lower cost. Cavitation-plate extensions offer the benefit of placing lift in the farthest aft spot possible, so that the greatest lift per square inch of tab surface is achived."
This article implies:
Although Cavitation-plate extensions cannot not be fine tuned like trim tabs,the same beneifts trim tabs offers to large boats the Cavitation-plate extensions give to smaller boats:
1)Faster Planing
2)More Stability
3)Better Hole Shots
4)Saves Fuel

I hope that this may have answered some of your quesstions. I am not an expert, I can only draw on my limited experience in comparing what my boat and engine have performed with and without Doel-Fins. Maybe Clark Roberts or Kingfish or some of the other memebers that have posted favoralbly on Doel-Fins could answer you queries better than I.

Clark Roberts posted 05-25-2001 08:17 AM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
As I have posted several times, I use Doel-Fins on all my motors (Currently 135 Merc, 40 Merc, 40 Mariner and 20 merc)! I would recommed them to all but the decision to use is individual. I would not recommend the cast Aluminum (like the Bob's Machine unit) or other rigid wings as they may break the anti-cavitation plate if hard object or extreme rough water is encountered! Happy Whalin' ... Clark,,, The Old Man and the Sea
alaskaTammy posted 05-28-2001 01:28 PM ET (US)     Profile for alaskaTammy  Send Email to alaskaTammy     
We have a 15 w/ a 85 yamaha. The dolfins throw up a weird spray. We don't like them.
scottfarm posted 05-28-2001 08:57 PM ET (US)     Profile for scottfarm  Send Email to scottfarm     
Took my Doel-Fin off last time out and it felt like my power steering belt broke. That's how much difference in made in the steering. Top speed was lowered due to engine cavitating when I tried to trim out to much. Those of you who are getting lower speed with fin simply need to raise your engine where the front of the Doel-Fin is just out of water while on plane. The boat is really a bear to steer without the fin.
daverdla posted 06-05-2001 11:49 AM ET (US)     Profile for daverdla  Send Email to daverdla     
I had posted earlier in this topic about my Doel-Fins causing the boat to list to port at high speed. I finally got the boat in the water this past weekend. I ran it with and without the fins. The boat runs true without the fins. For what its worth, I noticed that the boat does have a higher top end (~3-5MPH) without the fins.
lhg posted 06-05-2001 02:34 PM ET (US)     Profile for lhg    
It seems as there is some consensus coming together about the Doel-Fin issue. They help in achieving plane quickly, at lower speed, if that is what you need, while they are still running in the water. But it also implies that if this is needed, the engine should be raised so that they run in "air" once plane is achieved, so as to not drag down speed and otherwise hurt performance/fuel economy.

Clark, is this how yours are used, since I know you use elevated engine heights?

Clark Roberts posted 06-06-2001 07:33 AM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
Larry, all my fins run slightly above the water when on plane. My goal is to run on plane at the slowest possible speed but I also get easier steering as mentioned by Dennis Scott (Scottfarm). But all may not get the same results... it's that "personal choice" again! Happy Whalin'... Clark... Spruce Creek Navy
Whaletosh posted 06-06-2001 09:21 AM ET (US)     Profile for Whaletosh    

looking back over this thread I realized that I may have given you the wrong impression about the SE Sport foil. I have used that unit on 4 boats:

an older starcraft trihull

an aluminum 16 footer

a Dauntless 13

and a 13 Sport

all of the boats benifited from the foil except the 13 Sport. More trim range, better time to plane, less porposing, etc. and there was usually only a 1/2 statute MPH loss in top speed (GPS confirmed).

Just for whatever reason the combination of the 13 Sport and the SE sport foiul didn't work.


whalernut posted 06-06-2001 07:58 PM ET (US)     Profile for whalernut  Send Email to whalernut     
Thanks Sean, the Stingray Fin on my engine now works great! I just like the smaller Sport SE 300, the way it looks and the smaller size, maybee I should leave best alone since the Stingray works great! Regards-Jack Graner.
lhg posted 06-13-2001 04:37 PM ET (US)     Profile for lhg    
"boatdesigner" - if you are reading this thread, considering your experience with Whaler, etc, would you care to add your comments here?
Arch Autenreith posted 07-24-2001 02:49 PM ET (US)     Profile for Arch Autenreith  Send Email to Arch Autenreith     
Well, after buying a version of Doel-Fin ($35) and trying it I took it off after about 1 hour. Maybe that wasn't long enough trying but the one thing that I didn't notice anyone else say was, with mine, when I slowed from almost any speed the engine kicked up a bit and when I accelerated again the engine slammed back down against the transom. I don't have t/t so that particular issue wouldn't happen otherwise, right? And even though I had left the gps in the car I know (famous last words) it scrubbed a good 3-6 off the top.
Anyone want this? Seriously, if someone out there wants this as it may work well with thier setup let me know. Pay for shipping and it's yours.
Bigshot posted 07-24-2001 03:35 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
I have removed them from every whaler I bought except the 13's. I realize they will make planing quicker but my Montauk with a 90 Yammie gets on plane in about 10 feet. Not much out there planes faster, same with my 15/70hp. If you really need to plane at 12mph it is a good thing but my cruise is 3700 @ 28+mph and the fin does nothing and slows my top end. If you do not have PTNT then they can be a good thing or if you ski maybe but for overall cruising with enough HP, I never found them helpful on the smaller whalers. My buddy loves his on his 17 outrage and I love mine on my 20 Hydra sport, but my Whalers, Nah!
Bigshot posted 07-24-2001 03:44 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
PS I can stay on plane at like 2600, how low can you go with the fin?
Arch Autenreith posted 07-24-2001 04:18 PM ET (US)     Profile for Arch Autenreith  Send Email to Arch Autenreith     
Don't know. See my post in Repairs\Tachometer Bouncing dated 7-23. Am going to try to fix it after not working for about 3 years. But in my mind it didn't seem to make a whole lotta difference. Darn. I guess I have to make sure I have the gps and tach working from now on to be able to answer these types of questions in the future. I was fine without these things before. How come you all are making me fix everything! :)
Dick posted 07-24-2001 08:05 PM ET (US)     Profile for Dick  Send Email to Dick     
Mine is coming off befor the next trip out. It did get the Montauk on step a bit quicker but I lost 4 to 5 mph on the top end. I can live with it taking a couple extra feet to get on plane to get the top end back.
I had never run one on any boat I have ever owned and never recomended them to my customers or stocked them in my parts department. I have allways believed that a good hull with the proper power doesn't need a Doel-Fin, or such. Well I at least tried one.
Bigshot posted 07-25-2001 11:29 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
My 14 carolina skiff with a 30 Yamaha(rated for 25) is not drivable wihout the fin. It porpoises so bad(motor tucked in so far the bow drags)you would get sick. Doel-Fin and now it rides like a real boat and I can run the trim about straight. The engine is a 2cyl 30 so it is not the weight issue, just a crap boat and crap design. It is selfbailing though.
bc posted 07-25-2001 05:39 PM ET (US)     Profile for bc    

I found on out on those type of boats that moving weight foward goes a long way. They build them so light they are sensitive to weight while on plane. (although they can carry alot of weight) Most people (myself included) keep alot of weight in the back..trolling batteries, gas tank,etc. With my 16' sundance (carolina style) it came with a over-rated 40hp. Porposed bad until hydofoil installed. I downsized to a 25 merc which corrected the problem without the foil. Going from a 40 to a 25 was only a 70 lb decrease in weight, but considering that weight is hanging off the back it made a difference. For a person on a budget, I think carolina skiff makes a heckov boat. Great layout for fishing. Wish my 15' was as "fishing friendly".

Bigshot posted 07-26-2001 09:47 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Layout is great because you design it the way you want. Mine has the front deck, forward storage bench, console and rear bench. It is open and such but the handling is horrible along with the ride. Draws some water too. Great for kids and the 16 is a better ride. I think I would prefer a 17 or 19 due to the hull design.
Erik posted 07-26-2001 07:13 PM ET (US)     Profile for Erik    
You cant expect a flat bottom to cut though them get what you see...a flat bottom boat. I have to say they do have pretty fast hulls. A friend of mind has a 12' Carolina Skiff with 99' 25hp Johnson(tiller) that reaches 30mph, then when i get in the boat the speed doesnt change it still reaches 30mph. Im sure with a SS cupped prop it can reach 35mph solo. It has the foward deck and 2 bench seats.-Erik
Bigshot posted 07-27-2001 01:09 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
actually,no. One the boat is overpowered and 30 in that thing is dangerous. 2 mine is overpowered and 30 is dangerous(what it runs). If it had a 20 or a 40 on it, it would still run 30. Difference being I will still run 30 with 3 people in mine. And the 40hp would still do it with 5 people. Boats, believe it or not, have like a top speed for the hull, whalers and most other boats have it too. You have to double the hp to get a 5 or 10mph gain. Don't believe? A 13 with a 25 will do 30+ with a 40 it does 38?. A 17 with a 50 does 35, a 90 does 43. Big dif is with a 90 I can still cruise at 30 with 4 people, the 50 won't. Does this make sense?
Bigshot posted 07-27-2001 01:14 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Something else about bud has a J-16 with a 25(same as my 30)and he is faster. The longer the hull the faster it will go, when talking a displacement hull. That is why they built bigger ships back in the days, like the Titanic. Bigger meant faster. I am not a scientist and maybe somebody here is and can explain better than I. It ha sto do with physics and water displacement, etc. But a 16' boat that weighs the same as a 12' will go faster than the 12.
1987GTX posted 07-27-2001 02:21 PM ET (US)     Profile for 1987GTX  Send Email to 1987GTX     

when we bought our '87 guardian dive boat w/90 hp evinrude and loaded it up with 8 dive tanks and gear for 3 adult male divers in monterey, the boat wallowed horribly during holeshots. after living with this for ~10 dive days, i installed a Doel-Fin and the problem was reduced significantly... and the improvement was easily noticed when doing hole shot comparisons with a friend's non-fin configured boat. helped our waterskiing launches, too :>) our gtx has large trim tabs, or i'd add one on this boat, too.

be well,

Erik posted 07-27-2001 04:27 PM ET (US)     Profile for Erik    
Thats really strange how the flat bottom boats perform. I do remember my friend with the 12' carolina say that the speed was about the same with his old mercury 15hp. I have heard that carolina type hulls are the fastest and tunnel hulls like "TwinVee" are not as fast as you may think cause they cut the water to much...dount no if its true.-Erik
Ventura16 posted 08-06-2001 01:15 PM ET (US)     Profile for Ventura16  Send Email to Ventura16     
I've been trying to decide all summer whether or not I should bother to install the Doel-Fins I bought...because of the mixed results others had reported. Plus I've been reluctant to drill holes in my cavitation plate, and was afraid it would be a big pain for no gain. But I kept remembering how my Ventura 16 has been slow to get on plane and the Merc. 90 2 stroke has to stay trimmed all the way in most of the time, so I decided to go for it....

Well, I finally installed them, what a difference! It has completely transformed the handling of my boat. It gets out of the hole with no hesitation and the bow comes right down even with 2 adults and a large dog on board. I can trim the motor out quite a bit without porpoising at higher speeds and the steering is light and precise. I haven't yet checked the top GPS...but my subjective feeling is that it hasn't suffered much (if at all). I can only assume that the power curve, torque and weight of different engines are the factors that determine whether the Doel-Fin will work or not. I'm happy to say that in my case it made all the difference. I'm still investigating prop changes for even better performance, but for now I am one happy camper.


Bigshot posted 08-06-2001 02:30 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Good for you Tom. Like I have said, some boats it is a Godsend, others it hurts. Now that might not be true for the next guy with a 115, it is a trial and error thing.
Ventura16 posted 08-06-2001 09:31 PM ET (US)     Profile for Ventura16  Send Email to Ventura16     
It just goes to show that you need to try things for yourself. I had almost talked myself out of it, but figured that it was worth a shot. Many thanks to Clark, Kingfish, Dive1, B Bear, Sean (Whaletosh), and all the others who spoke highly of add-on planing devices...they definitely worked as advertised for me!

I have to take a minute to say that this forum is an ongoing source of high-quality information for me. Besides the Doel-Fins, in the last month, I've used the info here to install a transducer properly (thanks jimh), pull cables through the tunnel, drill holes without cracking the gelcoat, and so much more. My thanks to everyone who participates on a regular basis and to Jim H for running such a great site!


largej74 posted 06-26-2006 12:55 PM ET (US)     Profile for largej74  Send Email to largej74     
I read all the posts on here a couple of weeks ago trying to decide if I was going to do a Doel-Fin or not. I have a 17 foot Skeeter with a 150-HP. I was running a 21-inch pitch prop that would not get the boat out of the water so I switched to a 19-inch stainless. Still very bad performance and everytme I tried to turn the prop would have major blowout and you would come to a stop. Doel-Fin was installed this last weekend and it was a night and day difference. Gets up on plane probably three times as fast and now it even turns. This product actually made my boat enjoyable to drive and not near as much work.
hmbbuddy posted 06-30-2006 02:24 AM ET (US)     Profile for hmbbuddy  Send Email to hmbbuddy     
I use Doel-fin and I always fish on rough chops. When the chops goes down and flattens my boat planes and every chop gets shreaded like a weed. It is an old Montauk with 70 hp Johnson. On the plane the ride becomes steadier instead of being rocked from side to side.

I like it and I now have a Doel-Fin am going to put on my OMC outdrive on the 24 ft Searay even though I already have those planers.

Both boats are paid for so I can drill all the holes I want :)

JayR posted 06-30-2006 09:03 AM ET (US)     Profile for JayR  Send Email to JayR     
Although the motor on my ribbed Outrage has plenty of power and I need no help getting up on plane with a boat load of passengers and 2 Golden Retrievers I am still putting a Doel Fin on my new (GASP!) E-TEC 150.

A previous installation on an old Madetauk made such a difference in ride that I am convinced it will help on the Outrage.

I'll report back once I get a chance to try it out and compare....

Donald Altman posted 06-30-2006 10:26 AM ET (US)     Profile for Donald Altman  Send Email to Donald Altman     
Arch Autenreith I sent you an email. I am intrested in trying your doel-fin.. I think it is exactly what I need.


Kookadala posted 06-30-2006 06:42 PM ET (US)     Profile for Kookadala  Send Email to Kookadala     
I recently bought a SE sport 300 hydrofoil but have not installed it yet. The directions say to drill through the rotating trim tab on the back of my 81 Evinrude 200 to install it. Since I am taking the boat out tomorrow for the first time since I purchased it 2 months ago, I want to see how it runs before I install the hydrofoil.

Has anyone ever adjusted the rotating trim tab after the boat is first set up with the motor? Mine is set slightly to starboard, perhaps to compensate for the 2 batteries and kicker being on the starboard side of the boat?

When I bought the 80 outrage 21, there was no kicker on it, just the mounting plate. I am picking up a 15 hp kicker in 2 weeks and will wait till thats on before trying the hydrofoil.

an86carrera posted 06-30-2006 11:50 PM ET (US)     Profile for an86carrera  Send Email to an86carrera     
You guys just don't have enough horsepower. Slam the throttle for five seconds you back off and your cruising at 35?? a bonus you'll probably get better MPG.

And my daddy always said "don't use more than 2/3rds of what you got".


WT posted 07-01-2006 02:21 AM ET (US)     Profile for WT  Send Email to WT     
My fin makes my Montauk seem rock solid in the ocean. It eliminated my side to side movement in large swells.

Mine is a Turbo Lift made of heavy gauge 304 stainless steel. ?action=view¤t=DSCN1291.jpg&refPage=&imgAnch=imgAnch8


RussAdams posted 07-01-2006 03:55 AM ET (US)     Profile for RussAdams  Send Email to RussAdams     
After reading about Doel-Fins here last year I installed one.

It made a great improvement in performance. Keeps the bow lower on acceleration to plane. Gets up on plane faster. Reduced porpoising. All I could ask for.

1975 13-Foot Sport with a 1988 Johnson 40HP on a CMC PT-130. That's roughly 230 pounds on the 13's transom.

I'm re-powering this week with a 1998 Honda 40HP 4-Stroke. The motor has holes in the cavitation plate, so the previous owner had a fin of some sort on it. If I can determine which one by matching up the hole pattern I'm going to put the same fin on it too. Otherwise I'm going to drill yet more holes and put on a Doel-Fin.

That's how much I liked the improvement.


swist posted 07-01-2006 12:22 PM ET (US)     Profile for swist  Send Email to swist     
Tried them on two different motors and boats over the years. Came to the same conclusion as Powerboat Reports - it is the wrong way to correct what is more likely a problem somewhere else. Under/overpowered, wrong prop, wrong engine height, wrong trim, bad weight distribution, hull fault (hook or warp), etc, etc.
JayR posted 07-02-2006 03:30 PM ET (US)     Profile for JayR  Send Email to JayR     
I totally disagree with that mindset. I presently have no problems with my set up. Ribbed Outrage and a 150 E-TEC.

I'll guarantee that the addition of the Doel-fin will make the hull ride much nicer than it does presently. Not that there is a problem with the ride... most would find it more than acceptable. However, the addition will make the boat more stable on plane and reduce the bow slap in rough seas to almost non-existent.

Teak Oil posted 07-02-2006 05:52 PM ET (US)     Profile for Teak Oil  Send Email to Teak Oil     
I agree with Jay.

My Montauk is certainly not underpowered, and it certainly does not have a hooked hull lol. I tried mine for four weeks without the fin that came with the boat it is a flat out all around better boat with the fin on. Better handling, better ride, no top end penalty, etc. I can find no downside to mine at all.

pglein posted 07-05-2006 05:26 PM ET (US)     Profile for pglein  Send Email to pglein     
This is an interesting discussion. Let me submit my problem, and see what you guys recommend.

I have a 1971 13' with a 1999 2 stroke 30hp Yamaha. The engine is mounted on a steel plate I fabricated to raise it up (20" shaft on a 15" transom). The plate does not set the engine back or adjust trim, just raises it vertically (along the plane of the transom). The anti-cavitation plate is lined up just about perfectly with the bottom of the transom. A small amount of water comes over the plate, but I prefer it this way, as I've overheated an engine before and don't want to do it again.

With just me and one fuel tank, the boat hops on a plane plenty quick (4 seconds or so). But when I add a second person, and a full load of fuel, it's a lot harder. I usually have to lean forward over the console to even get it to plane. If I put a person in the bow, it's better, but with three or four people, it takes forever to plane simply becuase of all the weight. With just me in the boat (220#), my top speed is about 24 knots. I don't have a tach, so I don't know what RPM that is. I usually cruise at more like 19-20 knots on flat water, but in moderate chop, I have to fall back to 14 or less (to reduce pounding) and it often falls off a plane at that speed (especially with passengers).

I currently have a 9.875"x13" aluminum prop on the engine but have ordered a 10.125"x13" stainless replacement, which I am hoping will help. But I still have to deal with the inherent characteristics of the 13' hull. It is very suceptible to weight distribution and the flat bottom is very uncomfortable at high speeds in chop. Since the rear seat is the most comfortable (less vertical travel), this is where people prefer to sit when riding into chop, but this makes maintaining a plane difficult.

Would adding a doel fin help? It sounds like it probably would, but it also sounds like it would impact my already modest top speed.

I realize the real solution is a bigger engine with power trim. But I simply don't have $6,000 laying around. I need something that can be done for a few hundred, rather than a few thousand.

Or should I just relegate the 13' to tender duty and buy a Montauk for tackling chop? Again, I don't have thousands sitting around.

dandowneast posted 06-30-2006 09:35 PM ET (US)     Profile for dandowneast  Send Email to dandowneast     
I just put a 70-HP Yamaha two-stroke on my 15 STRIPER. Give me an opinions on the Davis Instrument's brand Doel-Fin.
BobL posted 06-30-2006 10:29 PM ET (US)     Profile for BobL  Send Email to BobL     
Gets you on plane much faster, lets you stay on plane at slower speeds.
bc posted 07-01-2006 07:42 AM ET (US)     Profile for bc    
I have a 50-HP on my 15 STRIPER and had a 70-HP on the same rig. Never had a need for one. With both engines the boat plans out easy and quick. I did use a Stingray brand on a 16 Carolina-Skiff- style boat with a oversized moter to control porposing. I hated drilling holes in the cavitation plate. When I put the correct horsepower on this boat, I filled the holes on the 40-HP engine with JB weld before selling. And didn't use a foil with the 25-HP. Personally I think they are ugly!
Livingwater posted 07-05-2006 01:03 PM ET (US)     Profile for Livingwater  Send Email to Livingwater     
SE Sport has a 200 Series which should work well with your set up. I'm planning to install a SE Sport 300 on my 150 XL Optimax.
RussAdams posted 07-07-2006 06:01 PM ET (US)     Profile for RussAdams  Send Email to RussAdams     
Peter (pglein):

I'm not an expert by any stretch of anyone's imagination, but it sure made a big difference with my 13-foot Sport.

Try a DoelFin. Boaters World has them for under 30 dollars. It takes at most an hour to read the instructions and install.

If you don't like it take it back off and fill the holes like JimH's link above says.

Truly not a big deal.

It's not going to make a 13 jump on plane with 4 adults on the rear thwart. But it will get you on plane faster, and should help with maintaining a plane at slower speeds.

There have been a couple notes here in Continuous Wave that indicate a fin will help keep water flowing to your cooling intakes, as it traps more water under the cavitation plate and closer to the water intake. Which should let you raise your motor a hole which should also help reduce porpoising, which might make the difference in the pounding your passengers get on the front thwart.


JayR posted 07-09-2006 08:15 AM ET (US)     Profile for JayR  Send Email to JayR     
At slow speeds in heavy seas, it acts as a vertical sea anchor and keep the stern down when overtaking large waves. The tendency for the boat to teeter over the crest of the wave, come down hard in the trough and slap the surface hard enough to rattle your teeth is just about eliminated.
With a doel-fin, the bow maintains a positive attitude and rides down the wave in that position allowing the boat to be in proper position to ride up the next wave (bow up).

If for no other reason, these appendages have a place on my flat bottomed, nut cracking, spine compressing, teeth jarring, slap happy Whalers. It takes away most of the hard ride they are so famous for. Certainly not the issues they are marketed for but a great side effect nonetheless.

HuronBob posted 07-09-2006 08:43 PM ET (US)     Profile for HuronBob  Send Email to HuronBob     
I installed a doelfin yesterday. I took the 130 sport (40 hp 4 stroke merc) out a few days ago with 5 adults (max per the rating), this is the first time I've had that many adults in the boat, with that load I couldn't get it to plane at all, and it has always been difficult with even four people.

I've not been able to test it with that kind of load yet, but I noticed a couple of things while out cruising by myself today: it planes in an instant now, the bow hardly raises at all with me in it, the ride is much smoother in my inland lake chop, and I can cruise at a lower speed...

I don't have a gps on the boat, but the top end seemed as fast as usual.

For the $30 bucks and 1/2 hour of installation time, it is well worth the investment...I should have done it three years ago when I bought the boat.

pglein posted 07-12-2006 11:54 AM ET (US)     Profile for pglein  Send Email to pglein     
I'm going to run with the new prop for a while and see what impact it has (installed last night), so I can get a good baseline, and then try adding a DoelFin. It can't hurt to try it.
kingfish posted 07-12-2006 07:20 PM ET (US)     Profile for kingfish  Send Email to kingfish     

I'm with you on this one - I really think you'll find a Doel-Fin will help with the conditions you described above. You may find that you'll want to raise your motor on the jack plate a little higher than it is now, so the Doel-Fin will clear the flow of water at high planing speeds. Short of doing that, you could experience some squirrely behavior at or near WOT.


rbruce posted 07-22-2006 09:56 AM ET (US)     Profile for rbruce  Send Email to rbruce     
I am a Doel Fin user. My Sport 11 and Chrysler 20 benefited from by getting into plane faster. I also agree with the rough water handling improvement and perhaps the top speed is about the same as before.

The only thing is that I no longer see the propeller and the exhaust coming from the exhaust snout!

Livingwater posted 07-25-2006 02:35 PM ET (US)     Profile for Livingwater  Send Email to Livingwater     
I'm having second thoughts about installing a hydrofoil fin (SE Sport 300) on my 150 Optimax. I just heard a story from my dealers mechanic that another owners outboard warranty was void because he had installed a hydrofoil fin on his merc.
pglein posted 07-25-2006 03:40 PM ET (US)     Profile for pglein  Send Email to pglein     

This issue has been addressed already in this thread. Your warranty will not be affected so long as the damage was not caused by the doel fin or improper doel fin installation.

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