Tabs & Motor Height Advice

[Out-Station]

G'day all, looking for some help on my ideas.

Wherever i go in my 6m C/C platey (Riptide) i seem to end up at full negative trim to get any sort of ride. At the same time, when running on flat water i start to get some cavitation and aeration with the motor (115 yammy 4/s with factory prop) running any higher the half on the gauge. Cav plate is basically dead level with the bottom of the hull at half on the gauge as per the pics.

1. I'm thinking i'll fit a set of tabs and drop the motor a hole at the same time what do you reckon?

2. Given my sealed tanks are right behind where the tabs will bolt on I'm thinking i'll get some alloy tabs (5mm plate) and hinges fabricated and weld them directly to the hull. Just buy the lenco actuators and controles etc. Anyone see any probs with this?

Cheer's Scott

[Bonus]

Scott, The motor's cav plate should be level with the bottom of the boat V - which it is so I would not drop it a hole or inch. If you drop the motor more there will be too much drag in the water by the shaft. I have Bennetts hydraulic tabs and I fitted them myself. Ask Dave at Riptide to weld on some mounting plates for the hydraulic rams and separate mounting plates for the stainless tabs which come with a stainless hinge. The new plates could be similar to the transducer mounting plates design. The tabs will change the boats ride completely and then if you still have problems you can play with the height of the motor later. My best motor trim position for cruising is just under the half position on the engine trim guage. let me know how you go. Russ

[Chimo]

Hi Scott

I'd suggest that you do one thing at a time so you have an idea whats causing what or whats fixing what.

Why not drop the motor one hole and try it before you add tabs. You can always go back to the current setup or drop it if its no better before you do the tab thing.

I'm really happy with my Lencos and I also have a foil on each motor too and my motors are set as high as I could get them BUT all of the above changes were made alone with a review / test run or two to see what the effect of the change had been.

You can adjust motor height using blocks under the motor fin and lifting or lowering the rear of the boat by winding or lowering the front of the trailer on the jockey wheel.

By the way if you were to fit foils, and things are set up right the foils run on top of the water surface when the boat is running at fast cruise or high speed with the motor trimmed up as you do for high speed running. I had the motors set up at the right height to achieve this on my Vagabond and then I fitted Lencos which also further improved fore and aft and side to side hull trimming.

Even with the lencos running up they do give an improvement which I guess is due to them effectively lengthening waterline / hull length.

Have fun, hurry slowly and good luck with it.

Cheers
Chimo

[Wahoo]

Scott, i dont see why PPL say the cav plate should be level with the bottom of the boat, all boats are different, my cav plate sits 40mm+ above the bottom of the boat, the dead rise looks to be 18+deg? for my liking i would lift the motor up, easy test, 1/2 load your boat, take it for a run in calm waters, 3/4 power, trimmed out to the sweet spot, have a look where the cav plate sitting, should be just above the water, if its under the water then it must be raised, see how you go


Daz

[ifishcq1]

Have to agree with Daz it looks like on that hull you should try lifting before even thinking of lowering .... aeration can be caused by the motor being too low
Scott

[FNQCairns]

O-S, Dont forget it's a tinny, plate maybe but still a tinny, are you expecting an unreasonably high quality of ride for the speed, so forcing forcing the nose down??
They have long pointy noses don't they? this gives a long overall length but can push the true wetted/planing length of the hull down toward a glass or pressed 5.4m boat - and ride is to a very large degree all about this (of coarse other things too) but if you cannot span the waves with wetted length any better than a 5.4......

If not then you do need tabs, will allow you to keep the nose down + keep thrust parallel with water surface.

You also need to find out just where the engine is in real time in setup, airation (some is ok, how much is up to you) at your forced traveling speed when in lumpy water will be the first indicator to drop the engine, until then higher is better up till a water pressure drop.

cheers fnq

[Out-Station]

Thanks everyone,

I reckon i'll go ahead and fit the lencos, use their tabs attached via some type of bracket. I'll leave the motor height where its at for the moment and see what happens. As was said above, it's only a tinny but given the C/C layout it does lack a bit of weight up fron't which impacts the ride to my thinking so i should see some benefit from the tabs.

I didn't know that aeration could be a result of the motor set to low so this is good info.

Has anyone ordered a lenco kit in from the USA, is so who did you go through, bloody expensive gadgets out here!!

Thanks again all, Scott

[Reel Blue]

Have you considered trying a different prop for the aeration issue?

[Bonus]

O-S, your cavitation may be caused by too much trim out. Half the guage is a fair bit of trim. Maybe your whole rig is becoming airborne. Russ

[sid_fishes]

why dont you see if dave can get onboard for a run before you start to spend /change things around. after all he built it so he should have several ideas about the issues you have raised. i,m not in anyway saying bad things about his boats[ i like them really] but i just think that hes the best person to ask cheers ian

[BM]

Out station,

Tinnies tend to ventilate if the cav plate is not level with the bottom of the keel extrusion. This is the standard fix I have adopted on lots of tinnies with issues.

Level with the bottom (or up to 25mm above) is the norm for a fibreglass boat as there is no keel extrusion.

Running with negative trim suggests that you are too heavy in the rear end and therefore 'flighty" in the bow.

Before trying to add more products to fix the problem I would be looking at the setup and seeing where the real problem lies. It could be a common thing for that hull or it could be specific to your setup.

Cheers