doel fin not working???

[digimortal777]

I run a 17.6 roundbottom boat with a 15hp johnson<br /><br />i put doel fins in the engine to help it plane.<br />It works fint upto about 3 quarters throttle or at full throttle with sumbody sitting up front.<br />if im on my own and i gun it it will plane lovely for abot 5 seconds, really fast......then all of a sudden the bow comes up and i havce a huge wake behind me with water actually coming in over the stern , what could be causing this, im thinkin of making fins and fixing them to the transom , most people here do that , but i need to figure out how not to puncture my boyancy tanks under the seat..<br /><br />anyone wanna make a suggestion feel free<br /><br />P.S<br />i have tried all trim positions , the midle hole seems to be the best , if i trim in for more lift it actually gets worse , and vice versa

 

[catfish1]

Re: doel fin not working???

a foil wont help a 15hp motor on a 17 1/2 foot boat, i dont think you'll ever get it to plane with that motor. you need more motor! just my opinion

 

[Jdeagro]

Re: doel fin not working???

Are you saying that the boat gets up on plane and then falls off plane? Once you are on plane it shold not be to hard to keep it there. Is the motor running out of fuel? What happens after it comes off plane ( stern drops and bow goes up), can you get back up on plane?<br /><br />We need more input!

 

[MajBach]

Re: doel fin not working???

I question whether or no this boat is actually planing to begin with. Are you sure? What speed do you think you are achieving?

 

[Maximerc]

Re: doel fin not working???

How heavy is the hull ? if it is a light weight Alum hull I might not be too suprized if the bow is being lifted out of the water by airflow. I had a 10 hp Merc on a 12 ft alum that was very light .. Lotta fun unless you got into some wind. then the front would lift so high you just freaked out and shut down the power.

 

[Dhadley]

Re: doel fin not working???

The motor's mounted too low. At the point the bow shoots up and the spray comes over the back is when the fin goes underwater. The fins were never intended to be run underwater. <br /><br />The whole idea of a fin is that it is a tool that allows a higher X dimension.<br /><br />This is a very typical scenario.

 

[Dhadley]

Re: doel fin not working???

ttt

 

[catfish1]

Re: doel fin not working???

Dhadley, all i can say is. you are the man! <br />i saw your replyThe whole idea of a fin is that it is a tool that allows a higher X dimension.) and went out yesterday and raised my motor some more. i never thought that since i am using a foil, that i could go even higher up than without a foil. i'm all the way up on my mount plate (2" above the bottom of the transom) and it runs fine!

 

[digimortal777]

Re: doel fin not working???

well i cant mount my motor any higher than it is<br />ill sort it out after september when i take the boat off the lake<br />probabaly make fins to oput on the back of the hull<br /><br />that what most folks do

 

[digimortal777]

Re: doel fin not working???

BTW catfish , it planed nicely with my old 9.5 , but the extra speed seems to be doing somthing funny to it

 

[Dhadley]

Re: doel fin not working???

Hey Catfish, Im glad it helped. <br /><br />They will do some very strange things if they get under the water. The whole idea is to reduce gearcase drag and improve effiency. That improves everything from holeshot to fuel consumption.<br /><br />Mr Digimortal777 -- there are many ways to raise an outboard motor. Even the small ones. Just putting a 3/4" or 1" board under the clamp brackets will help. Try it and see what happens. All it'll cost is a little time.<br /><br />Good luck!

 

[Jdeagro]

Re: doel fin not working???

digimortal777;<br /><br />Dhadley is likely to be correct. You should check to see if the new motor has a longer shaft than the old motor. The foil or any planing device should not run below water.

 

[bay5884]

Re: doel fin not working???

I'm pretty sure my foil runs below the water level on my 14' bayliner, 50hp force. I already have a problem where the prop will come right up out of the water though (usually running along with the lake waves when in between them). Should I bring the engine up to where the foil is just above the water line when stopped, or will this just make my situation worse? Thanks

 

[Jdeagro]

Re: doel fin not working???

Bay5884;<br /><br />The cavitation plate should be even with the bottom edge of the hull (bottom of the V) plus or minus 1". This would put the foil at the same level. When cruising on plane this should be at water level. Any planing device should be at water level when the boat is on plane.<br /><br />What are your handling problems currently?

 

[digimortal777]

Re: doel fin not working???

i might try a small peice of timber under the brackets n see how she goes , thatll involve a ittle work tho lol<br /><br />BTW both engines were short shafts boat is made for short shafts<br />15" transom etc etc