posted 01-19-2006 03:03 PM ET (US)        

a traditional "whale tail" type called a stingray
http://i25.photobucket.com/albums/c69/skiprobinson/stingray1.jpg

a bit more serious looking one called a hydro-fin
http://i25.photobucket.com/albums/c69/skiprobinson/hydrofin1.jpg

posted 01-19-2006 04:37 PM ET (US)            

My Montauk/90 combo came with an aluminum fin when I bought it. After a few weeks of running it I pulled it off and performance suffered in every way, including top end by about 2mph. I was surprised, I thought top end would increase while everything else got worse. I believe the fin allows me to run with a little more trim than I could without it, allowing for more top end.

I am telling you get a jackplate and a performance prop like a Laser II and you will hit 50 no problem. I would also add a fin not because it will make you faster, but it will help control the inevitable chine walking you will experience above 48mph.

posted 01-19-2006 04:48 PM ET (US)            

If you want a nice model that doesn't look ghetto, I'd check out the Bob's Machine shop stabilizer plate.

posted 01-19-2006 05:26 PM ET (US)            

Teak Oil, how high is your motor mounted? Is the AV plate above the water at moderate to high planing speeds? If so, in what way does (did) your fin interact with the water at or near WOT?

posted 01-19-2006 06:16 PM ET (US)            

If you want your Montauk to go faster you should raise your motor one bolt hole, loose the fin and buy a prop that has a little more grip.

posted 01-20-2006 07:18 AM ET (US)            

I do however appreciate the back drop scenery! Always above 65 degress in February in the apparatus bay! Priceless.

My outboard buddy once replied, when asked about these fins, "Don't you think the outboard industry spends enough money in R&D each year to determine if these appendages should be incorporated into the design of the outboard itself? Never really thought much more about them.

Spoke with Tarbaby who is running same outboard (2005 Yam. F60 4S EFI) mounted to transom of his 15 (not sure what year). He loves his. Running identical prop (10 1/4 X 15). Says he has not hit his rev. limitor yet. I believe he has not seen over 5700 revs.

Mine, 1982 15, with CMC jack plate, same motor, same prop, but very raised, will see 6100 running with the tide, and is hitting rev. limitor. Suggestions for a new prop?

posted 01-20-2006 06:42 PM ET (US)            

Tom you are correct in that at the time of my experiment my motor was mounted in the blind holes (before I purchased my jackplate) but this is a common installation for 17' Whalers, and with the fin I ran right near 45mph, and without it 43 was barely reachable. Its a lot easier to put a fin on than to raise the motor from the blind holes and get the same top speed. Also I got better planing, it held plane at a lower speed, and performed better in every way. Was my V4 OMC having a hard time getting the Montauk on plane? Certainly not. However it still performs better with the fin. When I took the thing off I planned on never putting it back on, but I just had to after the results I had. This was also when I was running the aluminum 13x19 OMC prop.

Now with the Rite Hite jackplate it is completely out of the water at speed and hits 47mph on occasion, so we are not talking about a tired motor either.

posted 01-21-2006 11:14 AM ET (US)            

Binkie, I'd LOVE a 115 on this boat but having just bought it, if I told my wife it needed a new motor I might find myself sleeping under the boat in the driveway all winter long. I appreciate your input.

runpastthefence, let me know how the jackplate works for you. I have been looking at the CMC one that has 5" setback and manual adjustment, its about $250 installed at my local marina.

posted 01-28-2006 12:54 PM ET (US)            

First, I'm not a fan of fins on classic Whalers. When I bought my 1988 Outrage 18 I was somewhat disappointed to discover that she wouldn't plane until she reached about 19-20 mph. She gets there real fast (about 3-4 seconds), and once fully on plane with the bow back down I can back off on the revs and she'll stay on plane down to about 16-17 mph, but I had been spoiled by my little smirkless 16, which would hold plane down to maybe 12-13 mph...nice in the chop and small windwaves. Anyway, I read through threads such as this one and consulted experienced OR 18 owners (Clark, Kriz, Goltz), all of whom recommended changeing props if I wanted to play around with lower on-plane speeds rather than using fins on the motor or trim tabs on the hull itself. I liked Tom Clark's salty reasoning the best--the classic Bob Dougherty OR 18 is a tried and true, successful veteran--perhaps the finest eighteen foot skiff ever designed--so adapt yourself to the boat and its design rather than screwing around with it...which is what I've done. No fins/tabs on my old girl, and now after I've spent many wonderful hours aboard in all sorts of conditions she has pretty much modified my seagoing design, rather than the other way around.

HOWEVER...

There's no doubt in my mind that for certain boat/motor/prop combinations, fins and/or trim tabs are very useful. There is just too much anecdotal evidence at this website and in every boating magazine I've ever read to ignore their efficiency in certain situations and with certain boats. As for direct testimony, when I see a boat (especially a Whaler) at the ramp or in the parking lot outfitted with fins/tabs, I usually try to elicit an opinion about them from their owner, and those opinions are universally positive. Now maybe those opinions are based on some sort of psychological need to be pleased with one's modifications and, in the case of tabs, to justify their considerable expense, but I can't remember ever talking with anyone who complained about the damn things.

Now here's where I get contrarian: Yes, in certain circumstances fins CAN increase the top end speed of a boat. My reasoning is as follows: When the fin is acting like a true hydrofoil and lifting the boat's hull out of the water enough to substantially reduce its wetted surface, it seems to me that the boat's speed could be significantly increased. I'll use as my example an article in the December 2005 issue of Sail magazine, entitled "Flying on Water" (pg 54), where the writer discusses the 60 ft long, 80 ft wide (!) trimaran l'Hydroptere, which reaches speeds of 43.4 kts (about 50 mph) blasting along on hydrofoils with her hull(s) completely out of the water...under sail! This weird, amazing craft looks like a huge three-legged water spider in the photo which accompanies the article, and of course any comparison with it to a Boston Whaler motorcraft is purely coincidental ;-), but the theory makes sense to my uneducated mind.

posted 01-29-2006 01:21 PM ET (US)            

There certainly may be Whalers out there that, because of the owner's naivete or choice, don't have their motors set at optimum performance height, and those are the ONLY ones that could exhibit a difference in speed at top end that is effected by the presence of typical AV fins. If your fins are able to affect top end speed, then there is something wrong somewhere else.

posted 01-29-2006 03:44 PM ET (US)            

Even on a optimally installed outboard engine, are you saying that a Permatrim with its shape and abilty to capture more of the propellers wasted upward thrust would not allow a higher engine trim angle therefore allowing a bit more WOT speed?

You must know from experience.....

posted 01-29-2006 05:13 PM ET (US)            

On an optimally installed motor, at high planing speeds, the higher (further out) you trim your motor, the further away from the water the AV plate (and consequently the fin) is. I don't have to know from experience that claims to higher speeds on optimally installed motors with Permatrim fins are fallacious, any more than I have to experience that water you pour out of a glass will not flow upward. (I *do* have experience with two Montauks, one 90HP and one 100HP, and an Outrage 22 (Evinrude 225) with DoelFins, and I *do* recommend them for getting up on plane sooner and holding plane at lower speeds, if such is your need. It is conceivable to me that Permatrim fins may work better under some circumstances than DoelFins in these performance issues, but it is inconceivable that either one has any effect on top end on boat and motor combinations that are set up as I described in my earlier post.)

Are you implying you can cite from experience on a Whaler (that is what we're talking about here - Whalers), higher top end speeds with a Permatrim fin on an optimally installed motor? Please bring on the details, if so.

I think for the sake of the other contributors here, you should disclose when you have a vested interest in a product under discussion. I note that your screen name is an acronym for Shipyard Island Marina, the only "USA Link" listed on the Permatrim website. And I'd humbly suggest you will sell more of your products by understanding in a better way what they can and can't do.

posted 01-29-2006 08:39 PM ET (US)            

First it is true that we are the US distributor for Permatrims and may I also say I absolutely did not post here to "sell" Permatrims or promote our business. What happened was I read something I did not agree with....so I posted.

Although it is true that Permatrims are not sold\promoted to enhance top end speed, I do know from several first hand occasions that they can. You want a Whaler test? Most recently this fall I installed a Permatrim on an 86-18ft Outrage with a Z150 HPDI Yamaha. Before the install I had a WOT speed of 47.5 mph trimmed up until the prop blew out. 45 minutes later after installing the Permatrim the boat hit 49 and some change and I had bounced off of 50mph on the GPS. I feel that the speed increase was a direct effect from the fact I could trim the engine higher. I don't think this is main reason to install a Permatrim but to say that it does not have an effect on certain boat hulls is just not true. Also at 50mph this 18 Outrage I feel is beyond its limits. The boat at this speed is very light and I was fortunate for testing that is was a flat calm day.

I think its safe to say that hitting 47.5 mph without the Perm with Z150 on an 18 Outrage, that the engine is mounted at the optimal height. Wouldn't you? Or is that in dispute now too. Here come the prop calculator comments......

I think I have a "good feel" for what Permatrim is capable of doing and not doing...Thanks for your concern though.

posted 01-29-2006 09:44 PM ET (US)            

You're welcome, but you've shown me that I have no need to be concerned for you (I wasn't, really), and I'm happy that you've been able to create a parallel universe where the laws of physics in this world don't apply. Apparently in that parallel universe Outrage 18s are beyond their limits at 50 MPH on flat water, eh? LHG, you must be glad you're in this world and not that one. And Buckda, I should think once you get your twin E-TEC 90s dialled in, you'll be happy to be in this world too...

deepwater, my Montauk ran pretty well with the Merc 100 and has continued to do so while my sister has owned it. I can't say it ran any stronger or weaker than the Evinrude and Johnson 90s I've had on the other Montauk though. I'll have to bow to the expertise of LHG on the nature of the Merc 100s compared to other Mercs, as that was the only Merc I've ever had.

posted 01-30-2006 09:30 AM ET (US)            

Let me re-phrase what I posted......50mph in an 18 Outrage is beyond my limits. Skippin along at 50 with not much hull in the water is not for me anymore.

Of course now if I was 20 years younger.......:^)

Gotta go.....Luke Skywalker and Captain Kirk are calling me.

Andy