Hydrofoils vs trim tabs

[Matal Mickey]

This is again old hot air as they say. If something is not broken, leave well alone. If it works as design and constructed, leave well alone, Famous proverbs. Why not ask the manufacturers you listed, the same questions. Why are they fitting from new, Trim Tabs??? A manufacturer that tells me his hull requires them for any reason whatsoever inc assist, enhance, change attitude, make it perform better etc,etc, then I will walk away to the next manufacturer and purchase the hull that performs correctly on it's own merits. That is not to say that for my own reasons I would never fit tabs. It may well be that I do not wish to move my cargo/passengers about in transit etc, etc. So I would fit whatever device I deem necessary as an aftermarket piece of equipment. Take a car for instance. Designed and constructed for general use as per the sales brochure and handbook/manual etc,etc. I select the one to suit my uses and purposes. Then I'm told by the manufacturer that I have to have an aerofoil fitted and mounted on the rear or front for that matter, to make it perform properly as per the handbook/manual basic performance figures and handling! I don't think so!!! I will go down the road and purchase the proper tool for the job, off the production line. Much simplier and cost effective, don't you think?
These items are very much personal bits of kit. It is not untill you realise that you have made an error of some type, incorrect purchase for application, bad hull, incorrect loading, incorrect seamanship, etc,etc that you have to go down this route. There is no clear difinitive explanation of this subject other than your own personal feelings and thoughts. I do however repeat my statement that a manufacturer with a good hull will not require any additives as such to make his hull perform safely and correctly at sea!

[ribit]

Can't see why you wouldn't want tabs and advise not to have them - everyone I have spoken to, from the dealer I bought the boat from - a main Yamaha dealer to people with SR4's on this forum, all say tabs work?! [/quote]

could not see the point of all the extra plumming required for trim tabs to such a small hull, as I made the comment more to go wrong, but as I said on your heading trim tab placement the ones you have purchased are keeping it nice and simple, and there given size relative to hull length should make a big difference

[wavecrosschris]

i think what i understand you are saying is Metal Mickey, in an ideal world with perfect weight distribution, perfect hull forms and perfect design we wouldn't need to use trim tabs?

But this doesn't exist?! (or maybe it does if your budget is bottomless?) somedays I carry 4 people on my RIB other days I carry just myself and fuel. Therefor for those days when i do carry a heavier load i buy trim tabs to adjust the hull dynamics for the extra weight - I don't think you can say just because a hull isnt designed with trim tabs it should never have them fitted.

The manufactures i listed are fitting them because they also know that everytime you go out in a boat something is different, whether it is the sea state and wind, or just amount of people on the boat.

My problem is that I have changed the characteristics of the boat through my own necessity to add equipment and weight and will install trim tabs to counter-act the problem - this is exactly what they are designed to do and surely the reason for having them?!

[Matal Mickey]

Yes, indeed we are both saying the same thing. I also have stated that to move cago/passengers etc and weights around is necessary. I am not as you think against trim tabs, to the contrary they are a fantastic after market addition. I simply critise a manufacturer who has to fit these after market additions to make his hull handle correctly and safely. A manufacturer of a hull and the type of engine/drive system fitted to that hull, with regard to RIB'S, will have taken into account the amount of trim available and required on the drive system in relation to his hull. Nowhere in any of these calculations during this process are trim tabs deemed necessary and or taken into account. Thats because the manufacturer has built and designed his hull for the vast majority of uses and functions, fitting the correct engine/s with the correct amount of trim for that hull. You state that you require trim tabs for a full or partially loaded boat. Surely you are able to use the standard power trim system incorporated into your drive system, thats obviously if you have a power trim systen on the drive? If not then yes, I can understand your dilema, its a bit of hit and miss utilising compromise.
Thank you.

[jwalker]

Originally Posted by Matal Mickey

....You state that you require trim tabs for a full or partially loaded boat. Surely you are able to use the standard power trim system incorporated into your drive system,....

Engine trim and trimtabs are not equivalent. Engine trim changes the thrust line and so wastes power pressing down or lifting the stern. It also changes the drive characteristic because the prop is changing depth in the water as the trim is adjusted. Trim tabs allow the balancing of the boat longitudinally and laterally to cope with windage and sea states. The engine can then be trimmed to give best thrust.

Sea states are so varied and variable that it is impossible to design a hull which will be satisfactory for every eventuality.

Foils have the added advantage of preventing the stern lifting and, therefore, the bow falling. This gives good longitudinal stability and is particularly noticeable when driving into a head sea where the wave length is a little too long for the hull length. The stability prevents the bow falling into the trough and uncomfortably impacting each wave front.

On twin engined rigs, the foils have a marked lateral effect in stabilising the boat in beam seas. If space between the motors is an issue, one foil can be fitted to the outer side of each anti-ventilation plate.

Just IMO, as usual.

[Sunfish]

So going back to my original post, as I can't move passengers, kit, weight etc
you'd all recommend trim tabs over hydrofoils.

Many thanks for everyone's input.

Regards,

G250

[wavecrosschris]

I would go for foils, I think if you have a SIB with a small outboard up to about 15hp they probably are the ideal solution. I thought about hydrofoils for mine but have gone for tabs as they just seem a more rounded 'proper' solution to the problem - I have heard stories that you can get flex from the hydrofoils when cornering at speed, one wing will bend down and 'dig in' and through the boat causing something unexpected - not sure if this would happen with a rib as they obviously don't bank over as far a hard boat...but thats just what I heard from someone in the trade.

I've only ever heard good things about trim tabs!

[Rodan]

How about non powered smart tabs, how do these compare?