Prop Fins

[Gnasher]

i have 2 fins attached just above the prop on my yammy 28HP that are designed to help my boat plane, but i have been told that having these attached will increase the fuel consumption. Is this true? and how much extra fuel would you expect to use? Do most of the other boaters in the club use these fins? (sorry, dont know the technical word for them so fins will do). Also will it increase the speed using these by much? Im just trying to work out whether or not i need them or not.

 

Dan

[Paul D]

Dan,

 

Fins didn't work for me on the Orkney but that is a semi-displacement boat.

I think you will find that you will lose a little on the top end speed ( more to drag through the water ) but will get on the plane quicker.

 

I remain to be convinced that they will improve fuel consumption , but as they didn't work at all on mine ( made the boat unstable ), I am not talking from practical experience.

 

 

[Newboy]

Some are known as Doul (?) fins. They are said to improve hole shot but once up on the plane, as it 'cut' thru water, it's one more drag on the boat so it worsens the fuel economy. Also different design have different effect on boat, I used to have one that looks like an aeroplane wings, ie., horizontal for a bit then up at an angle. I found it made the boat lean to one side.

[Adam F]

Take them off and try them, see if difference. They may work they may not - it depends on the boat. Yes you will loose top end speed, but it may make the boat plane quicker and hold the sea better - it did on Tara.

[Swainiac]

Dan, speaking from a non boating point of view, I monitor fuel consumption on the company vehicle quite closely, and have yet to return endurance anywhere but inconsistant! I dont drive at warp factor ramming speed.....unless going fishing of course, and find that different runs produce different mileages. I drove back from Derby...and gave a return of over 500 miles for the tank........on similar runs of similar distance, Ive returned far far less, the shortest distance being 265 miles!!

 

It follows that sea conditions are never identical, wind speed, tide speed, boat weight, etc, so I doubt vey much that your fuel consumption will vary drastically unless you are accurately measuring useage in the first instance. New engines tend to run better once worn in, then gradually worsen over the ensuing years of useage, so I doubt whether you'll trully know if the fuel consumption alters to a significant degree, unless you strictly monitor what goes in.

 

Rich

[Seamouse]

The Doelfin manufacturers claim they improve fuel consumption, not increase it. Warrior said not to fit them (165 with Mariner Bigfoot) as they didn't help and could make the boat unstable at speed. Conversely, a friend has them on his 150 and swears by them. He likes to run with the bows trimmed well down and they allow that. He doesn't get the annoying slow front-rear po-go at speed on the flat that I do, but he did without the fins fitted.

Why not whip 'em off and see what the difference is? Only a couple of bolts.

 

Steve

[duncan]

Dan,

 

would simple add that if they worked for every set up the engine manufacturers would fit them as standard.

 

most hulls are designed to operate best at a particular speed or speeds, and at a particular attitude - if you want to operate at different ones they (fins) can be a great help.

 

with regards to Steve's porpoising there was a long thread on that subject here about 2 years ago - as it normally only occurs at the upper end of the boats speed and trim (out) fins are rarely the answer (because of the drag) ; trim and weight distribution everytime.

 

try it with and without - for general pick up, ride and handling not top speed.

[Gnasher]

hi guys, many thanks for all the advice, i suppose i wont really know the difference until i take them off and see. I would of thought that they would of made the fuel consumption better because they help the boat plane at a lower speed and there for get most of the hull off the water and there for out of the way of strong tides, where as if it wasnt up on the plane the drag would of been increased because there is a lot of hull to pull against. im just being a tight ar$e and trying to scrimp on fuel costs. trial and error is the key i think

by reading a few of the threads, i think that more prefer to go without them, then with them

[Bob F]

I've tried with and without them on my 70hp fitted to SO (Alaska 500).

 

I love em!

 

She definitely gets up on the plane quicker, especially noticed when the boat is fully loaded.

 

But best of all, I have much more adjustment on the engine trim which gives a better ride.

 

They probably work on my set up because a 70hp is a fairly big (heavy) engine for an Alaska 500.

 

I have lost about 4knots on the top end, but this is no big deal. How often can you do 32kts anyway.

 

Don't know if it's affected the fuel economy, because as Rich says, each time you go out the sea conditions are different. My gut feel is that it is slightly better on fuel economy.

 

BF