Hydrofoils worth the bother???

[davidni]

Well....seriously enjoying my new SR4. Haven't even managed a solo trip yet as my boys are glued to the rib!

Took them out for their first session on the donut\ringo\biscuit (everybody has their own term) and they had a blast.

But it just left me with a query....

My youngest despite being the daredevil in the family, is not just as confident in the water as his older brother.

He prefers being towed at a much slower pace.

Problem is, the slow speed means the nose is well up whilst towing him at the slower speed, even with his brother perched at the front doing lookout duty.

I was wondering if fitting these hydrofoils would help with getting the nose down a touch more at the slower speed? Not expecting miracles at such slow speed but getting the nose down a touch would be nice.

Now, if you think these would do the trick, could anybody recommend a quality product ...or warn of any to steer clear off? And do they have any negative effect on the ribs general handling?

There will be a fair bit of watertoy towing as the boys love it and the rib was boat as much for them as myself.

Just thought I'd ask outright on here as research throws up all sorts of opinions...and I would rather get some first hand, present day opinions.

I know there is the minefield of prop choice that could be discussed but tbh the standard Tohatsu prop No 11 seems a well matched all rounder.

I will say this...it pulls the toy with absolute ridiculous ease...in fact when it gets one the plane, I have to back off a fair bit immediately as it really ups its momentum significantly in a matter off a few secs. Despite me being told by a few people that 40hp would be adequate but not ideal for pulling the donut!

For reference, the engine is a Tohatsu M40C.

[jonp]

Theres a reason you lose your warranty on any engine over here with them fitted, they put extra pressure on engines steering bearings etc.

Ive owned fibre glass boats with them and while they do as advertised they can also exaggerate boats bad habits especially in rough conditions, where a boat can be hard to recover on big side on swells.

Ive found these self levelling trim tabs to be far more effective and much safer Self Leveling Tabs (SLT) | Bennett Marine

Jon

[Starovich]

Used them for year on different boats, do what they say on the tin, plane a lower speed, encourage bow to drop etc.
Ive never had an issue with steering,or felt any il effects. My current boat has has them fitted and has done for 15 years, seems to still be functioning fine .

Years ago had a 4m dory, heavy old thing wouldnt plane with the 15hp we had lying around at all, until we put on the dolefins then it worked OK, slow but it planed.

They are like bovril, either you love them or hate them, and you wont convince either camp to change their mind.

[jonp]

After moving from the IOW to here (Aus) I soon found comparing the seas I used boats on over there are a little different from here. When I say they are dangerous in rough seas Im talking about large ground swells with big breaking waves, in these conditions most people wont be out in their boat but we do get caught out occasionally.

Has anyone asked any manufacturer if new engines are fully covered under warranty with them fitted over there, if not why not.

Have a search Pro's & Cons of hydrofoils on outboards you will find many people describing the effects I mention on non rib boats in rough seas. Ive owned boats that Ive happily had them on but only used those boats in mainly calm seas.

Self levelling trim tabs are simple and cost much the same, they also let you adjust each side of the boat differently to correct for prop torque or an uneven load (console and batteries on one side etc). Full electric (hydraulic) trim tabs become much more expensive and trickier to master.


Jon

[davidni]

Those trim tabs look interesting. The self adjusting ones with no electrics hydraulics etc.

Thanks for that...I will look into this a little more.

The rib planes very quickly on a whole. And many inc Tohatsu have advised that the standard prop really is the best match for the engine regards all round usage hence was looking at other avenues.

[Starovich]

Having used small boats with them on in up tom btf 8/9 ive never noticed any untoward handling characteristics that were not down to using a small boat in silly seas.
Admittedly ive never done back to back tests (done out with dolefins on tested, then come back taken them off and tried again), but i cant say ive ever felt a bad sensation that i could attribute specifically to them.

Dole fins £25
Trim tabs £90

As to prop size, a one size fits all prop would seem to me to be a strange thing to say, will it work of course. Put the same engine on boats of different weights, styles/hull config you will get a different result. as long as the engine is running in optimal rpm range then most props will do. but will not be optimal.

You can play with this to see what you get Prop selector

[davidni]

Yeah, completely fair point.

Should have elaborated...have been advised that the standard prop suits the SR4 well for general all round pleasure usage.

Not having a lot of experience yet on the rib just thought I would avoid starting to mess with props just yet. Had just wondered about the fins as a simple aid.

The boat planes very very quickly. It's just my youngest is comfortable at what I consider a very slow speed and it would be good to just get that nose down a touch more without causing issues elsewhere.

I appreciate the feedback and welcome anyone's opinions as many on here seem plenty more knowledgeable than myself.

Seems like one of these options will work.

Just for reference...I doubt I will be in any silly seas in the near future. Fairish weather only unto such a time as I have the experience to confidently.handle a bit of weather.

And I haven't a chance of getting out without the boys for now...will take some time for the novelty to wear off them, I'd imagine.

[Poly]

Do you have power trim (or could you manually trim down when he is ringo-ing...)

[Starovich]

Originally Posted by davidni

The boat planes very very quickly. It's just my youngest is comfortable at what I consider a very slow speed and it would be good to just get that nose down a touch more without causing issues elsewhere.

bag of sand /container of water in the bow?

[davidni]

Originally Posted by Poly

Do you have power trim (or could you manually trim down when he is ringo-ing...)

Its just manual trim.

Tbh the boat seems to go well trimmed 2 up. Power trim would be nice to be able to adjust as conditions change.

Trimmed ot right down for it. But the speed he's confident at is really too slow to expect the boat to keep its nose down without some sort of additional help.

And when its nose up for long periods, it seems to drink a bit more fuel.

[davidni]

Originally Posted by Starovich

bag of sand /container of water in the bow?

I wish there was room!

[davidni]

All being said...this is the most fun I've had with the kids all year!

[Last Tango]

Bag of sand in the bow will have a lot more adverse effects at other speeds/conditions than the fins will. I've found that the effect of "Doel Fins" is marginal but definitely marginally better for getting "out of the hole" and at speed they have absolutely no effect one way or the other as they aren't even touching the water.
Compared to the mass and thrust of the engine hanging on the back of a boat bouncing in and out of the water the additional loads imposed by the "lift" from a pair fins is trivial and IMO would not generate any significant additional stress on engine mounts or pivot.

[Xk59D]

4 blade prop maybe worth a looksy rather than fins.

cheers

[jonp]

Do you have propeller dealers like solas props over there ? After talking with solas out here they told me of many people who had had issues with foils on engines and strongly recommended not using them.

One particular boat I was wanting to use for towing the kids in donuts etc as well as offshore game fishing with slow to midrange trolling they recommended a smaller pitch 4 blade stainless prop (expensive) but it did make the boat handle way better. We have an extremely dangerous bar crossing where the extra grip from the 4 blade meant getting through way easier.

I would put the smart tabs on my 550 pro but unfortunately theres not enough room on the transom after fitting two transducers and a live well pick-up. When I was mentioning the cost being about the same I was talking about the se sport fin not the dolphin cheapy.

Jon

Jon

[Starovich]

Originally Posted by Last Tango

Compared to the mass and thrust of the engine hanging on the back of a boat bouncing in and out of the water the additional loads imposed by the "lift" from a pair fins is trivial and IMO would not generate any significant additional stress on engine mounts or pivot.

Hydrodynamics are a powerful thing, relatively small foils create a lot of lift. the effect of a wing is more pronounced in water than air.
Check out the size of the foils on an AC45

Foiling

or a Waterskipper.

[Last Tango]

"Hydrodynamics are a powerful thing, relatively small foils create a lot of lift. the effect of a wing is more pronounced in water than air.
Check out the size of the foils on an AC45"

Without actual figures it is difficult, so I'm not going to stand on a soap box to get shot down but.......
I figure the "effect" is roughly equivalent to about 50Kg sitting in the bow and if we assume the effective centre of gravity to be about a third of the way down the length from the stern then, the "lift" force required to produce the same effect would be 1000N. As the engine probably already weighs around 100Kg, 1000N is simply supporting the engine's own weight leaving the imposition on the bracket at zero. Ask yourself...would I lift the engine by these plastic fins, how much more weight would they lift before they broke.
IMO they would 'fail' long before the engine mountings would.
As I say, all sort of guess work and I'm not advocating that they're the solution to his problem.............the 4 blade prop sounds interesting.

[jonp]

Still doesn't answer the question if manufacturers still give full warranty if they are fitted and whether they recommend them. We can all have our opinions and personal experiences with them but none of us are experts in the field where Yamaha, Suzuki, solas etc are.

[Poly]

Originally Posted by jonp

Still doesn't answer the question if manufacturers still give full warranty if they are fitted and whether they recommend them. We can all have our opinions and personal experiences with them but none of us are experts in the field where Yamaha, Suzuki, solas etc are.

Given that the involve drilling holes in the anti ventilation plate no manufacturer is going to warrant them. I've never seen any official guidance from a manufacturer suggesting bearing issues, have you? Can you share it with us?

If they were universally great then manufacturers would offer different leg designs with bigger plates built in. That they don't tells me that they arent needed by a big part of the market.

[Xk59D]

You don't need to drill for fins if you don't want to-

You have a couple of options, couple are below depending on the mounting method you want.

Force 4 Marine Dynamics Stingray Starfire Hydrofoil

http://www.force4.co.uk/force-4-stin...B#.Vat0EShwbMI

https://youtu.be/AoDFQwyRSxY

Cheers