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

Simon B · 20 July 2009, 10:09

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 · 20 July 2009, 10:13

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 · 20 July 2009, 10:19

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 · 20 July 2009, 10:37

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 · 23 July 2009, 07:48

Does anyone know how going astern with trim tabs works?

Does stern dig in?

Steve_B · 23 July 2009, 08:36

Quote:

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 · 23 July 2009, 10:10

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 · 23 July 2009, 13:16

Quote:

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 · 23 July 2009, 15:16

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 · 24 July 2009, 13:35

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

BumbleAbout · 02 August 2009, 09:09

Quote:

Originally Posted by kelson

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.

Smart Tabs ... an excellent way to help a boat get on the plane at slower speeds.

On my Futura Mk 2, I ended up doing lots of manual trim adjustment last week with the Doelfin - not good !

How slow can you get on the plane with the Smart Tabs ?

Rogue Wave · 02 August 2009, 09:36

It would be tabs for me.

I don't like the thought of drilling holes and bolting on extra stress point to the AV plate.

Observer · 03 August 2009, 08:46

Quote:

Originally Posted by BumbleAbout

How slow can you get on the plane with the Smart Tabs ?

Haven't got them yet but hoping for 10-12 kts.

I have 6m RIB with Yammy 90. I haven't done this very accurately but on flat water (tidal Thames) 18kts seemed to be the lowest speed at which I was 'properly' planing. On the sea I was planing at lower speed, maybe 12-15 kts. That seems counter-intuitive so possibly it was my feel of where the boat was comfortably planing was a bit different.

I've ordered the Smart Tabs with the optional retractor plate kit, so, when I have them fitted, I'll be able to test with tabs and without in identical conditions.

adams1x · 03 August 2009, 20:46

I used the doel fins on an Avon 5.45 Seasport I owned once on a mariner 90HP, the arrangement on that boat is that you are sitting at the back, I kept it on the hamble and on the long wind up the hamble I often went out on my own, about 4 / 5 knots you couldnt see over the bow when seated!

Once I fitted the doel fins they were amazing, minimal bow lift, faster planing and vision at lower speeds! Made no noticable difference to the top end. Sure if you are launching the boat out of the water off waves and totally being airbourne i am sure the extra platform on he cavitation plate would not be good for transom etc but that is not my normal ribbing so they worked well for me :-)

Simon B · 04 August 2009, 09:23

We used Tigershark VG fin on last boat and it did work well, however, I do still dislike the idea of drilling the AV plate. I'm sure if fins were the best solution the tab manufacturers what be out of business.

The replies so far have certainly tipped me toward favouring tabs, we haven't taken delivery of the boat so we do not know yet whether we will need anything, forwarned is forarmed.