doel fins how do they work?

[markg]

my engine has doel fins fitted if i understand correctly these are to get the boat on the plane faster but i dont quite understand how they work, does the tilt angle of the engine make much difference to the way they work and do they work by digging in and raising the bow of the boat or am i completely wrong
confused of telford,

[simmons0]

They create lift at the stern...thats it really. Lifts the stern helping it plane earlier.

A nice extra is that they increase response to the trim as well.

[Poly]

Originally Posted by markg

do they work by digging in and raising the bow of the boat

the opposite - a bit like a plane's wing they create lift.

[m chappelow]

i tryed some on one of my small sibs a few weeks ago and they did not make any difference at all ,much suprizing to me infact they slowed me down a couple of knots , we tryed the engine pos but it did not make any difference so i took them off and had the speed back ,i not saying they dont work on some boats as most boat owners that have them say there great ,the guy who came out with me has some on his boat and they work great ,also heard that they can put vertical strain on the engine swivel moutings and bushes over time on certain engines . the only good side it made steering a bit more responsive . but i now have 4 holes in the anti cav plate .

[simmons0]

Well in creating that lift its going to cause drag so generally you will lose a couple knots off your top speed.

[jyasaki]

They also prevent aeration by some degree, by shielding the prop from sucking down air from the water surface.

They seem to affect different boats in radically different ways. Some will show no affect, others will perform much better with them (or similar.) No idea as to why.

jky

[captnjack]

They mostly prevent aeration at holeshot, slight amounts of stern lift at medium speeds (like an airplane wing), should be close to out of the water at speed or they will kill your top speed.