Hydrofoil query again..............sorry.

[180shabah]

Re: Hydrofoil query again..............sorry.

My 19' Bayliner Ski boat (Cobra style copy) with a 125hp Force outboard came with a Doel fin hydrofoil. I ran the boat a coupla times just the way it was, then at a later date took the Doel fin off. I noticed it took longer to get on plane (even though this hull design is made to plane off fast & easy for skiing), it also appeared that the boat had more lift without it, causing it to become airborne from the chop, and slam down hard more easily, and finally in turns the boat leans quite a bit now, and I might have lost 1-2mph, but it is negligable, considering the disadvantages I experienced without it. Next season I intend to put the Doel fin back on, because I like the out of the hole improvement, plus the boat staying more planted in the water (instead of going airborne at times at higher speeds), and finally, staying more level in the turns on plane, and I'll accept scrubbing a bit more speed. It appears to work for me, at least for now, until I get smart tabs to compare.

Sounds like you already got a set of tabs in your future, so I am not going to push them at you. But I do want take a moment and examine your observations, because they are 100% normal.

Foils provide large amounts of stern lift, which is why they make your boat almost jump on plane. They DO NOT stop lifting afterwards though. As the stern lifts more and more, the bow gets pushed down. You plow through chop nice and smooth. This is biggest cause of lost top end speed.

In a turn with the bow "planted" the boat has a tendancy to rotate around while leaning less. Feels good, more like your car. However, this ain't your car, it's a V-hull boat. Leaning into a turn is a good thing. The flatter angle combined with extra lift makes a high probability that in an aggressive/evasive maneuver that the hull will trip, or dig the outside chine into the water. This can send gear and people flying, possibly being thrown overboard, or in extreme conditions(very rare) the boat can capsize.

I know, i'm giving you all the gloom and doom, but they are poorly engineered band-aids that can be dangerous. There are boats put there that a foil is the perfect solution for, but they are the exception, not the rule. 'Foils do exactly what they are advertised to do: Decrease planing time, offer a smoother ride, lower minimum planing speed..... The problem is what they do that is not advertised, and people mistaking it for good "handling".

Sure 99.9% of the time the smooth ride worth the decrease in both economy and top speed. But what about that log that you didn't see until the last second, or that jetski that suddenly takes off straigh into your path, either one forces you into a hard turn and a possible disaster.

 

[ondarvr]

Re: Hydrofoil query again..............sorry.

If used correctly, a fin won't slow you down or create handling problems, the problem is you can't really set it up correctly with an I/O. The problems most people encounter using a fin are in not changing anything after they bolt it on, they just bolt it on and head for the water, used this way it has little chance for success. The fin shouldn't be in the water when on plane, with a fin it can be possible to raise the motor a hole or two and reduce the drag from the lower unit, resulting in a higher top speed. With the motor raised this high the prop would normally ventilate badly under acceleration and the fin will (may) help reduce it.
With an I/O you're very limited as to what you can change, so the results won't be as good as they might be with an O/B and there's a very good chance they will be negative in many areas.

I'm not a fan of fins, and what normally is needed are tabs, but they can work when used correctly.

I had a fin sitting in my shop for years, and while trying to get the setup right on my 19'CC I was running into a bad ventilation problem as I raised the motor. I could most likely have solved the problem in a better way for several hundred $$ by trying a few SS props, but I don't use this boat that much and didn't want to spend the money on one. The fin worked very well, I gained a couple of hundred RPM, increased my speed and improved my planing time for no money.

 

[MikDee]

Re: Hydrofoil query again..............sorry.

Foils provide large amounts of stern lift, which is why they make your boat almost jump on plane. They DO NOT stop lifting afterwards though. As the stern lifts more and more, the bow gets pushed down. You plow through chop nice and smooth. This is biggest cause of lost top end speed.

In a turn with the bow "planted" the boat has a tendancy to rotate around while leaning less. Feels good, more like your car. However, this ain't your car, it's a V-hull boat. Leaning into a turn is a good thing. The flatter angle combined with extra lift makes a high probability that in an aggressive/evasive maneuver that the hull will trip, or dig the outside chine into the water. This can send gear and people flying, possibly being thrown overboard, or in extreme conditions(very rare) the boat can capsize.

My bow is not plowing, nor is it planted, the whole boat settles into the water better,,, without it, it is "skittish" at higher speeds, and it still leans in a turn, just less with the fin on, so I doubt it will catch an outside chine, & trip, in a hard maneuver,,, what do you think this is a hydroplane with hard chines?,,,lol,,, been there, done that, in my youth

 

[180shabah]

Re: Hydrofoil query again..............sorry.

My bow is not plowing, nor is it planted, the whole boat settles into the water better,,, without it, it is "skittish" at higher speeds,and it still leans in a turn, just less with the fin on, so I doubt it will catch an outside chine, & trip, in a hard maneuver,,, what do you think this is a hydroplane with hard chines?,,,lol,,, been there, done that, in my youth

Hydroplane? Nope.
I was assuming the boat in question was a v-hull bayliner, like the one on your in your sig.

 

[b_a_kickboxer]

Re: Hydrofoil query again..............sorry.

Let me start by saying I've used both. When I purchased my boat (used) it had a hydrofoil on the I/O. Was I happy. I really didn't know the difference. What I did know is that that a friends boat with the same engine always was up and out of the water quicker then I was and his boat always seemed to handle much better then mine. I took the hydrofoil off for half of the season and really couldn't tell a difference. I started reading this board and heard about "Smart Tabs" and ordered a set. Nothing is scarier for a boat owner, whether it's a $600 or $60,000 boat, then to drill holes in the transom. I was no exception to the rule. The instruction were reasonably clear and with drill in hand I had them installed in an hour or so (most of the time was spend worrying about what I was doing). I have a 18' BR and completely gutted the boat and rebuilt it myself over the winter. Of all the money I've spent on the boat this was the best investment I've made. It now jumps up on plane, no bow rise, and handles like a dream in turns. The handling at idle in the marina is even better, no wander. I did have a few questions and issues before and after installation and John was quick to respond. He even exchanged the actuators for me to better fine tune, free of charge. Would I buy another pair? I'll have "Smart Tabs" on whatever boat I own from now on. The hydrofoil is hanging in the garage as a constant reminder to check the board first before making a foolish investment.

 

[QC]

Re: Hydrofoil query again..............sorry.

I love this guy ^^^^ FWIW if you like Smart Tabs and also like taking control of things, you'd love helm adjustable tabs Either way, tabs on ALL V-hulls for me!!

 

[NSBCraig]

Re: Hydrofoil query again..............sorry.

Hey just wondering a few things after reading this thread.

Are you using you trim motor? I know it kind of sounds like an odd question but then just about every time I go out on someone else's boat more times then not they have no real trim or even throttle control, just lowering the motor in the water and pushing the throttle forward to some set point.

This has been the cause of every bad handling boat I've been on. I know this cause they handled just fine with me at the helm.

My point is boat manufacturers spend a great amount of money designing and setting up their products, so the first thing you should probably consider is wether or not your boat is the way the factory set it up or not.

Is it at the correct x dimension (prop height)? What about the prop? Is it the same as the factory matched up with your hull and motor?

If it's not, it's not going to work right no matter what performance add on's you throw at it.

I think it becomes kind of like souping up your Camero in high school- at these headers plus this cam and these gears oh and i have to get a tunnel ram with dial quads. What you and up with is a hard starting, gas guzzling, car that runs slightly faster then stock when it does run. I know I need drag radials that will do it.

As for top end though ALL drag is bad be it foil or tabs.