Doel fins & prop pitch

Doel fins & prop pitch

Post by Elie Garfink » Wed, 22 May 1996 04:00:00


Hi,

Can anybody out there tell me if this is a valid solution? Here's the problem:
I'm running a 20' bowrider with a Merc 4.3LX and a 21" prop. It's very easy to
over rev this setup, but I need it to pull up a 200 pounder on 1 ski. I don't
want to lose my holeshot as it stands now, but I don't want to have to be
constantly watching the tach so's not to over rev, (nor do I want to shell out
a fortune for a variable pitch prop) My solution: Bolt on a doel fin and go
back to my 23" prop for top end and fuel economy(if it planes faster, then I
should get better acceleration with that fin) It would be really great if I
could get my 56-57 mph top end back with the 23 incher, and still haul up that
slalom skier. What do you think?

Regards,
Elie Garfinkel

 
 
 

Doel fins & prop pitch

Post by Larry A. Fishe » Thu, 23 May 1996 04:00:00

Elie, as one who has used Doel fins on two entirely different boats I can
offer you my experience and advice. I think Doel fins work great on
smaller boats, ie., 50hp and below motors on boats up to 16 feet. I had
one on a 50hp Nissan that was mounted on a 17' Aluma-weld. It worked
great and got on plane in an eye blink. I sold my fishing buddy on them
and he finally put one on a 90hp Nissan mounted on a 17' VIP tunnel hull
bay boat. The results were that it did not change a thing - absolutely no
effect. Well, I traded boats and got a 19' Hydra-Sport Hydra-Skiff with a
112hp Johnson. I immediately put a Doel fin on the motor and found the
same as my buddy - absolutely no effect. To make a long story short, I
put Bennet trim tabs on my boat (my buddy followed suit) and the results
are truly amazing. I can come right up on plane without the back end
setting way down in the water. It's very nice to come up on plane level
without the bow pointing to the stars. Same effect on my buddies boat. A
side benefit is that the trim tabs allow you to stay on plane at lower
speed. I find this quite usefull sometimes. They also act like after
planes and really smooth out the ride on bigger boats. Kinda like shock
absorbers for boats! They are not cheap, but I believe they are really
worth the expense.

Larry Fisher


 
 
 

Doel fins & prop pitch

Post by Steve Leinwa » Fri, 24 May 1996 04:00:00



Quote:
>Hi,

>Can anybody out there tell me if this is a valid solution? Here's the problem:
>I'm running a 20' bowrider with a Merc 4.3LX and a 21" prop. It's very easy to
>over rev this setup, but I need it to pull up a 200 pounder on 1 ski. I don't
>want to lose my holeshot as it stands now, but I don't want to have to be
>constantly watching the tach so's not to over rev, (nor do I want to shell out
>a fortune for a variable pitch prop) My solution: Bolt on a doel fin and go
>back to my 23" prop for top end and fuel economy(if it planes faster, then I
>should get better acceleration with that fin) It would be really great if I
>could get my 56-57 mph top end back with the 23 incher, and still haul up that
>slalom skier. What do you think?

>Regards,
>Elie Garfinkel


Elie,
Doel fins (and all the clones) work great in two situations:
1. the boat is stern-heavy, and there is no way to redistribute
   the weight

2. the boat is underpowered, and re-powering is impractical.

If you need the 21" prop to pull a 200 pounder out of the hole, then your best bet
is to keep it on there, and watch your tach carefully. Otherwise put the 23" prop
back on for best top speed. a 20' bowrider (approx weight ? maybe about 3000 lbs)
with a 4.3 V6 is a marginal combination for deep water starts with 200 lb skiers.
The Doel Fin will lift the stern, but unless that 23" prop will allow the engine
to rev up to it's power curve, your acceleration will suffer, as will fuel economy,
and engine wear.

Best bet is to get your skiing buddy to go on a diet !

 
 
 

Doel fins & prop pitch

Post by Lawrenc » Fri, 24 May 1996 04:00:00


Quote:



>>Hi,

>>Can anybody out there tell me if this is a valid solution? Here's the problem:
>>I'm running a 20' bowrider with a Merc 4.3LX and a 21" prop. It's very easy to
>>over rev this setup, but I need it to pull up a 200 pounder on 1 ski. I don't
>>want to lose my holeshot as it stands now, but I don't want to have to be
>>constantly watching the tach so's not to over rev, (nor do I want to shell out

<snip>
You can also get a rev limiter.  Racing boats use them so that they don't
overrev when airborn.  You set the top rpm.