Lifting Foil (Doel?) or Trim Tabs (Smart?)

[Simon B]

Of the two above options which one is better, I have experience of boats with/without lifting foils but none of trim tabs.

Just a hypothetical question at the moment.

[chewy]

Are you on about doel fins which bolt to the leg? Fitted some to my Dads Aquabell and it made a knot or so of difference. Wouldn't bother on a RIB though.

If I had the choice I'd go for trimtabs. Is it for your RIB? If so whats the problem?

[PeterM]

doesnt this enter the realms of ;

2 stroke v 4 stroke ?
big launcing wheels V small ones ?

I have them on my 4m RIB as its easier then drilling into the hull ( for tabs) & I dont really have space on the transom for tabs . Its pretty stern heavy & yes I loose a couple of knys off top speed , but you really cant do max speed in anything except mirror calm seas. So maybe 1% of the time I use the boat. But for the lower planing speed ( 12 down to 9 knts) and much much reduced bowlift & better trim response I like the doelfins.

[Simon B]

No problem yet, boat not arrived.

Yes I'm on about comparing Lifting Foils (bolt to AV plate on leg of outboard) vs Trim Tabs fitted to transom especially the auto adjusting types like Smart Tabs.

My question is of two which gives a better enhancement/correction to boat performance. Had good results from lifting foils to correct for a slightly heavy engine. May need this time to help heavy boat onto plane, thats after all things prop related get ironed out so may not be an issue in the end.

[Simon B]

Does anyone know how going astern with trim tabs works?

Does stern dig in?

[250kts]

Originally Posted by Simon B

Does anyone know how going astern with trim tabs works?

Does stern dig in?

Simon
I have the SmartTabs on my rib, whilst I have never used the fins, I cannot fault the tabs.
After over a year of use, I did wonder if they were of benefit, so recently disconnected them and had a trip out. The difference that made was very noticable and all, including the crew, agreed to put them back on asap. Not that the boat was any where near being bad, just that with the tabs the ride was so much better, quicker to the plane, a plane speed of 10kts, softer landing if we got some air.
As for going astern, its not something most ribs do very often and when we do, there is no digging in at all, as the speed is low and then angle they are set at is not steep.
The reason for fitting is that out of Poole we had a long run at a max speed of 10kts, before the tabs, this meant about 15mins of the engine pushing hard at sub planning speeds and a nose up attitude. With the tabs, I can get on on the plane quickly and by playing the throttle just keep it up and not break the speed limit.
Regards

[Simon B]

Cheers 250kts, that was exactly the kind of information I was looking for. Boat not delivered or sea trialled yet so still do not know if anything is actuallty required.

The intended use would be a dive rib (as per signature) tabs look like they would be good on this type of vessel. We do not have the luxury of a monster motor so may not retain plane on grunt alone. Our Delta was prone to being knocked off the plane by fairly small swell.

[codprawn]

Originally Posted by Simon B

Does anyone know how going astern with trim tabs works?

Does stern dig in?

The QL interceptor tabs wouldn't!!!

[kelson]

I have a SIB rather than a RIB, but I have run both a Doelfin and Smart Tabs on my vessel. The Doelfin worked fairly well, but I had to trim the outboard more forward than I would normally to get the fin to have the desired effect at slow speeds. It was necessary to fine tune the trim at different speeds and attitudes to get good performance. Not too difficult with power trim, but I was constantly adjusting the trim to get the best result. I don't like fins on my shaft for one big reason, they are great at catching kelp! Here in San Diego along the coast we have a lot of kelp and it is thick enough to catch you even when running at relatively high speeds. Tabs don't have that issue. I rarely have kelp grab a hold if I'm running at a reasonable speed with trim tabs. Smart tabs work well for me and the automatic adjustment is very convenient. It is easy to add a small pulley arrangement so the tabs can be raised when you need to back down and manuever without interference. This is a big issue for me as I beach my Futura a lot and the lowered tabs can dig into the shore and be damaged. Raising the tabs also makes it easy to load on a trailer with bunks that extend past the transom without hitting the tabs. Certainly not a substitute for properly distributing the weight in your vessel, but an excellent way to help a boat get on the plane at slower speeds.

Tabs in raised position (the yellow tape keeps the fittings from rattling when loose)

[Observer]

Well I've just ordered Nauticus Smart Tabs so will measure performance before and after and report. Watch this space.