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Author Topic:   Doel-Fin Cure For 130 SPORT
sanjaun2 posted 05-31-2004 10:06 PM ET (US)   Profile for sanjaun2   Send Email to sanjaun2  
I just purchased a new 130 SPORT with a 40-HP two-stroke. I noticed the boat porpoises a little at speed when in choppy seas. Would one of those doel fins on the outboard help? If so, do they help or hurt the top end speed? A reply from anybody with experience with this on a new hull style 130 SPORT would be appreciated. Thanks
jimh posted 06-01-2004 08:46 AM ET (US)     Profile for jimh  Send Email to jimh     
[Changed TOPIC; was "2004 13 sport".]
Moe posted 06-01-2004 09:07 AM ET (US)     Profile for Moe  Send Email to Moe     
The further down on the boat the motor is mounted, the greater leverage the motor's thrust has to lift the bow and create porposing. The motor should be mounted with the antiventilation plate at, or slightly above, the bottom of the transom. Raising a motor mounted too low is often enough, by itself, to stop porpoising. Having the motor up is absolutely critical, if you have a Doel-Fin. If it runs submerged, it will create drag AND can increase porpoising when trimmed up.

Are you trimming all the way down when taking off, and trimming down some in chop, so the bow can cut through the waves, rather than be lifted by them?


sanjaun2 posted 06-01-2004 12:29 PM ET (US)     Profile for sanjaun2  Send Email to sanjaun2     
Thanks for the reply, I am trimming down when it starts getting choppy. That does help quite a bit, but it still porpoises a bit and with the trim down the speed is greatly reduced. I was hoping that a fin would reduce that and keep me skipping on the wave tops.I will go check the height of the motor. I just assumed that it would be right since this is the package whaler has come up with.
jimh posted 06-01-2004 08:37 PM ET (US)     Profile for jimh  Send Email to jimh     
Newer Boston Whaler boats are rigged at the factory with the motor height on the transom set to the proper position and the engine equipped with a suitable propeller. Previously, when a dealer did the rigging, there could be much greater variation in how the engine and propeller were set up.

Any boat can be made to exhibit a pitching oscillation ("porpoising") in certain wave conditions, engine trim, and boat weight distribution. It is not that hard at all to get into a state where an uncomfortable pitching motion begins to oscillate. Any boat will do it at some point. Some are more prone to it than others.

Before I'd start adding $29.95 plastic fins to the motor, I would become more familiar with the way the boat handles, and experiment with different setting of the engine trim, as well as different weight distribution in various sea states.

boxers posted 06-01-2004 08:50 PM ET (US)     Profile for boxers  Send Email to boxers     
We had similar trouble with our 1998 40th anniversary 13 footer (a 13 GLS hull with a blue interior). We added a 40 HP Honda and the additional weight exacerbated the problem further. The stingray fin we subsequently installed provided an immediate cure. Now passengers can move fore and aft without any problems. Just a touch of trim and the bow goes right where the captain wants it to.
Too bad all our boating problems weren't this cheap to remedy. Good luck
sanjaun2 posted 06-02-2004 03:01 AM ET (US)     Profile for sanjaun2  Send Email to sanjaun2     
thanks for the replies, I think first I will experiment with the trim and loading and then buy a fin if needed. I was not worried about spending 30 bucks on one, spending money is what boating is about right??? I didnt want to drill holes in the outboards cavatation plates if I didnt have to. But now I know there is at least one happy camper,I will not worry about that so much.
sanjaun2 posted 06-02-2004 03:06 AM ET (US)     Profile for sanjaun2  Send Email to sanjaun2     
Hey boxers, did the fin have any effect on your top end?any pro's and con's other than you mentioned? Thanks and happy boating!!!
lpaton posted 06-02-2004 07:25 AM ET (US)     Profile for lpaton  Send Email to lpaton     
The fins sticking out the side make cavitation plate vulnerable. Hit a relatively small object and you snap off the cavitation plate.
I have played with weight distribution and motor height and porposing is mostly gone on Outrage III except with full (and I mean full) load.
billyc posted 06-02-2004 07:35 PM ET (US)     Profile for billyc  Send Email to billyc     
I have a similar hull (2000 13 Sport) with a 25 hp fourstroke. I had no problems with porpoising.

I added a fin because it allowed me to get on plane quicker and cruise on plane at a lower speed. My wife and I are old (with bad backs) and find that 15-20 mph in this boat is much more comfortable than 25-30. I also use a low pitch prop (11") because of a heavy load. I found that top speed was not affected by added the fin under my operating conditions. Both of my problems would probably be eliminated by more hp but it was easier to put on the plastic than exchange engines.

It was difficult for me to make the decision to drill those holes. I think the fin stayed in the package for three months before I actually did it.

Every now and then I take it off just to see which configuration I like better. I end up putting the d____ thing back on each time.

kbshoaps posted 06-02-2004 08:12 PM ET (US)     Profile for kbshoaps  Send Email to kbshoaps     
Look at the Turbo-Lift if you don't want to drill holes.

I described the improvement to my 150 Sport last month.

NO decrease in top speed and several other enhancements make it a good choice.


jimh posted 06-02-2004 08:14 PM ET (US)     Profile for jimh  Send Email to jimh     
Although I do not own a doel-fin, and I have never installed a doel-fin, I am impressed with the unsolicited testimonials from users of doel-fin's.

There must be something to this $29.95 piece of plastic, else all these guys would not be swearing by it.

On a small boat I can see how it would be prudent to test this theory with a $29.95 bet, versus wagering about $600 on trim tabs.

Moe posted 06-02-2004 09:16 PM ET (US)     Profile for Moe  Send Email to Moe     
From what I've seen, Whaler mounts the 40HP two-stroke as far down on the transom as far as it will go.

I'd sure try it up a notch or two up before perforating the AV plate. May as well do it first, because with the fin in the water, it WILL add drag and decrease speed, as well as contribute to porpoising, and you'll probably be raising it anyway to cure that. What kshoaps didn't mention is that he'd already raised the motor to put the AV plate above the bottom of the transom before he installed the Turbo-Lift. That's why he didn't lose any speed.

There's also a lot of evidence on this forum where raising the motor one notch made a big difference in performance, including eliminating porpoising.


sanjaun2 posted 06-03-2004 02:57 AM ET (US)     Profile for sanjaun2  Send Email to sanjaun2     
thanks again for all the replies and pictures! I am new to whalers and im finding this site and its knowledge very useful, I should have time this weekend to play around a little and experiment. So i,ll keep you posted on my decision and its results. I am baseing all this on my neighbors boat. same as mine except its a 2002. I actually just picked up mine today and only have 15 minutes run time on it, Damm its so clean and shiny!!!! I to have a bad back so everthing I can do to help the ride is worth it, My body has a hard 42 years on it but my mind is still in its teens and wants to play!! I am going to west marine tomorrow to pick up some bottom paint and those hull protector strips that you bond on the leading edge of the hull.
arnereil posted 06-03-2004 07:50 AM ET (US)     Profile for arnereil  Send Email to arnereil     
I have the 13 sport, also. Raised the motor up and put a block of wood on top of transom to help hold it. My purpose was to try to get the rpms up above 5k with the stock prop. I gained about 250 rpm. I do have a doel fin on it as well. The boat takes more time to get on plane than my old aluminum 16 footer because of the bottom shape. The 13 has a small water foot-print with quite a bit of front overhang, I belive to help balance the motor weight..... It is a 13' after all, any weight affects it quite a bit...... In a week or so, I'll be adding my bimini top and moving the battery to the left side of the boat under the front seat..... The battery and I on the same side of a small boat makes it lean. A full tank of gas, at 40 pounds in no way offsets a 200 pound human and a 35 pound battery.... and down the road I may gain a stainless prop if things work out well...
GeneNJ posted 06-03-2004 09:58 PM ET (US)     Profile for GeneNJ  Send Email to GeneNJ     

How will you handle the cable lengths with the battery repositioned?

boxers posted 06-06-2004 08:02 PM ET (US)     Profile for boxers  Send Email to boxers     
Been out of town so to answer your question sanjaun2 about top speed I am not sure if it was effected. The fin surely causes some drag but since the boat is easier to control the trade off was worth it on the 13 ft BW. The "stingray" fin design has a brace that connects the two sides so it lessens the chance of fracturing your cavitation plate. I hated to drill holes in the cavatation plate but can't say enough good things about effects of the stingray fin. I later put one on my 18 foot Pursuit and had poor results? Not sure why but I expect the boat was just too big (2000lbs) for the benefits to be felt. I the case of the Pursuit it did feel slower at WOT.
bw12 posted 06-06-2004 10:31 PM ET (US)     Profile for bw12    
boxers, do you mind me asking, did you use the "Stingray Junior" model, which is rated for motors up to 40 HP, or the regular sized Stingray? Thanks in advance.
ocuyler posted 06-07-2004 04:58 PM ET (US)     Profile for ocuyler  Send Email to ocuyler     
I installed the Stingray "senior" on my 03 16D. It reduced bow rise, improved speed to plane and can reasonable plane at 15 MPH or less. The motor is one hole up. The fin lifts out of the water at cruising speed and above. I noticed better overall performance and no negatives.

I had no reservations drilling holes on the cav plate. They can easily be filled.

Highly recommended.

cmac posted 06-01-2007 01:11 PM ET (US)     Profile for cmac  Send Email to cmac     
Have an 87 VIP bass boat w/ a 115 Merc. When at top speed it planes.,but when I slow it down it starts to porpoise I keep it planed all the way down. Any clues?

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