Foil observations

[Owen]

I have a 4.55 Quintrex Escape with a 50hp Mercury on the back.
It came with a foil on it when I bought it (brand unknown, but quite large).

Recently I had reason to remove the foil so I could work on the leg, so I thought I'd give the boat a run without it to see what difference it makes.

This boat has always seemed to me a bit bum heavy, so I have never been surprised it was fitted. I have tried several different leg heights with the foil on looking for the sweet spot and feel where I have it no is the best overall.

On taking the foil off I noticed;
Getting on the plane takes longer and the nose up attitude is much worse :(
The boat can turn much sharper and faser without cavitating.
The wake is a LOT cleaner without the foil, suggesting it is in the water at palning speeds, yet when I raise the motor more it cavitates too easily and becomes VERY trim sensitive.
I noticed one more thing which is perhaps too subjective and would require more testing back to back in the same conditions, but I mention just to see if anyone else can confirm.
i.e. I am sure the boat had a "softer" ride without the foil. We mainly get short chop up here, not swells, so you tend to smack from one wave to the next. Being bum heavy I'm thinking with the foil the boat comes down on her bum and the foil makes the front slam down harder than when it's not on.
Like I said, it's pretty subjective and would require testing on the same day in the same conditions to confirm.


Overall, I prefer to have it on, but it did leave me wondering if I might be better off with;
a smaller foil
Perhaps a foil that looked like a V from the back. My thinking is it would still provide lift out of the hole yet wouldn't lift the bum it turns, so might decrease the cavitation without me having to trim right in on turns.
A bigger boat..... Sorry every problem I have can be solved by a bigger boat. At least that's what I tell the missus ;D ;D


So has anyone had similar results to me?
I'm aware every hull/motor/foil combination is different, but just thought it's be interesting to hear from guys & gals that have actually done before and after tests rather than the usual "my mate had one" typ of advise.

cheers,

Owen

[Chimo]

Hi Owen

Re foils

a bigger heavier boat with foil runs flatter so the bow works better to use its vee and "slice" thru water better.

A heavy boat with fins and with trim tabs works better still as any lean that results in the boat not running on the Vee is overcome.

With out tabs but with fins a heavy boat won't use its Vee bow and hits on the flat of the side rather than the bow.

I've noticed these things in my boat a Seafarer Vagabond as initially it had neither foils nor tabs and I fitted them seperately and with some time between.

I wonder if your motor / boat would no longer cavitate but still give the overall advantages you have decided to keep if you lifted your motor one hole?

With the weight and length and hull shape of your boat (tinny) I think there is only so much that you can expct from the hull in the range of water conditions you describe.

So much is going to depend on speed wind, the lean of the boat with a canopy and clears fitted particularly if the boat is not fitted with tabs. Then again it gets to a point where a bigger boat becomes a better, safer more comfortable proposition.

This was my argument (won) in upgrading from a 5.6 Express tinny to the Saefarer Vag. The express had a foil, had tabs and was a very good seaworthy boat but I tended to run it a little faster in the sort of chop you describe and there was nothing else for it but to go bigger.

I have no doubt there wil be a range of opinion on this but these are my own results over 15 or 20 years with a few boats. Hope they are of interest and help to you.

Cheers

Chimo

[GAD]

Gday mate ,
just got back from Fitzroy Island, and I have to tell you I lost 10kph from the se300 I put on ,on sat, dropped 500rpm, watched me mate that I normally sit beside pull away , hey don't like that , so its coming off,

[Owen]

GAD
I saw no appreciable difference in top end. In fact if anything I got an extra 1-2 k's with it on.
That's so little a difference that it's more likely to have been wind, tide differences.

Maybe you need to lift your motor a bit. To drop that much top end the foil must be creating significant drag at planing speed.
I've tried mine in different positions ranging from well below the keel to well above it.
In fairness I didn't do the same thing without the foil.

Did you perceive any difference in ride quality?

cheers,
Owen

[GAD]

No , ride was much the same but a little quicker out of the hole , but my main objective was to try it but I can do better without it .....

[BilgeBoy]

I have been batteling cavitation issues of late....removed the foil and raised the engine...now she is spot on, Yet to put the foil back on to try...but my guess is it will help. I have a 4.35 Front steer with a 50Hp and without it is a little unstable in the front...same thing...the back feels kinda heavy!!

Originally, my foil was a good 1/2 - 3/4 of an inch underwater at cruise speed...Where is yours??

BilgeBoy

[Chimo]

BB

Foil needs to be a tad above water surface when your cruising with the motor trimmed back / up. Otherwise my experience has been lots of resistance / spray and possible loss of speed /efficiency.

Have used them over many years on a number of different boats to lift bum, impove hole shot, improve stability on small boats with big motors that otherwise feel they are going to tip over when you move the tiller even a little. Turns boat into a sports car in that situation that turned like it was on rails, eg light 10ft tinny with 9.9 HP

Cheers

Chimo