Hi folks

My 47” Lynx mono is fitted with a starboard trim tab to counteract the torque roll. And although it runs well it does every now and then have a tendency to submarine. I figure that a down side of trim tabs is that by lifting the transom up it can pull the bow down.

As an experiment I decided to fit two wedges on the starboard side of my hull.

I figured that these would offer the following advantages over trim tabs:

1 Less drag as when flat out they are not constantly in the water.
2 Importantly the front wedge gives hull lift when the bow is wet such as in turns. The other wedge acts closer to the C of G keeping the hull level.

Today was my first run with this set up. It was the best my Lynx has performed todate. For the first time in 2 years of running I could throw sharp 90 degree turns at full throttle with confidence.

I will be keeping these little wedges as they worked very well for me.

These images show the boat and the wedges subsequently fitted:

Cheers
Craig

That's a great idea. I used to do it when I raced big boats, but by NAMBA rules, it's illegal.

Hi Steve

Out of interest, what wording in the NAMBA rules makes such wedges illegal?

I had a look but could not find anything relavent to this.

Cheers
Craig

Not positive but, i think these would be considered as the hull being stepped and stepped hulls are illegal.

If such a modification makes that considered a stepped hull, then by the same reasoning a retractable trim tab mounted in the hull (say mid ship) would surely also be illegal.

If so would that question the legality of trim tabs used anywhere on the hull?

Craig

Looks like a lot of induced drag --- I have a few Mono's without trim tabs - secret alway been a extremely sharp prop with well set up strut and never had major issues with prop walk

Not sure I would do that to a good boat ....... I would try other props and turning before I glued plastic to running surface of hull

No Offence but seems like a bandaid solution to a non exsistant problem -- guys are looking to go faster by smoother bottoms and u have prop walk issue so u glue plastic "trim tabs" to bottom . Kind of extreme to me.

Problem may be cured by good prop, change of prop or strut setting

JMO nothing more .........

RD

NAMBA does not allow steps or brakes in the planing surfaces. Transom mounted tabs are behind the planing surface and are legal. Would have to agree with Hot Rods about other things being done first. C/G,drive angles,trim tab adjustments,props,etc is where I would have worked on. JMO.

In tne NAMBA rulebook under HULL CLASSIFACTION Section "G" Paragraph 2b) states "A hull has no discontinuities between or steps the wetted surface."

I think those shingle looking wedges would be considered discontinuities in the wetted surface.

Hi Guys

Thanks very much for your feedback and interesting comments.

I accept the illegality point thanks to the information given.

To pick up on the points from RD (and no offence taken at all):
Having experimented with 6 different props all are finger cutting razor sharp plus balanced so no issue on that front.

The wedges are actually carved from timber not plastic.

The strut setting on this hull has been experimented with to give the best combo I can find. I also adjusted the rudder angle backwards (at its base) to help prevent the bow getting too low in turns.

However in choppy water there remained a tendency for occasional totally unexpected submarining. The wedges touch wood seem to have made a big all round improvement without compromising straight line speed. Also cornering is more reliable and faster because I can keep the throttle fully open.

For this particular hull design I believe they have corrected a problem.

Cheers
Craig

Hi Craig
SO I'm curious if your friends boat (same boat I believe) has same "sub" issues - my Razor did that till I changed CG went from 33% to 34.5% and changed side to side balance. A turn fin was huge help in corners as it wanted to sub coming out of corners.
To me if it's not props and the issue is 'subing' then I would look more at CG (maybe move CG back and slight down on right side tab) and I would look at side to side balance. Does it sub turning left and right or just right?
I balance my boats now side to side (hang by line front center tip bow and center transom) and adjust side to side balance.

Wood or plastic still seems something is off to have to do that to a hull..

JMO

Randy

Watch how Razor dances side to side - and subs at end of video ---- cured with turn fin and change of CG