Lower Unit > vrs < Water Flow

[SIBRider]

Particularly higher RPM at lower height does not add up. Even if performance suffers at excessively high motor position because of ventilation. Engine is free to spin even faster.

[Locozodiac]

Stubborn Sibrider,

Knowing having a different type of inflatable than the post was meant for, why don't you post your own findings instead of taking for granted my water tests and keep contaminating my near whole post with your issues.

If you are happy with your combo performance which seems not, Alleluia. May the Northern Waters be with you...

Happy Boating

[Projectile]

Locozodiac:

In your experience, after sea trials with SIBS, what is the usual range of heights of the AV plate relative to the bottom of the transom that usually produces good performance and the type of lower end water flow that you appreciate?

I'm thinking that my ETEC 30 will have to sit with AV plate about 2 inches below bottom of transom on my WB465 to get rid of ventilation. Is that something that you commonly find, or would that be unusually low, in your experience?

[Locozodiac]

Proyectile,

Let's see if we can work this out together, I'm more than willing to do so. Will need to forget all about AV plate sitting on a dry installation as all engine owner's manuals blindly recommends. Dry engine setups most times doen't work properly once boats are tested on water at speed/plane.

Regarding inflatables for a perfect setup you have to deal with tubes diameters, transom heights and engine brands, all of which doesn't match between fabricators. Imagine all engine brands fabricating a dedicated engine that matches all inflatables sib/rib brands models.

Go to the other side of the pond and read this new post, has new info added, let me know if you fully understood at least the plain AV plate brand theory starting second post.

Opt Engine/Transom Height - iboats Boating Forums

Happy Boating

[sparky666]

Honwave 4.0 with 20 hp merc 4 stroke on the transom splashed like a shower , raised the motor 18 mm , no more splashing and now hitting 6000rpm a gain of 200rpm
Downside some cavitation on cornering and in choppy seas also my hole trim settings only give higher or lower than 90, I opted for higher as I don't like to plough
Great topic that through my own Experience totally accurate
Keep up the good work

[Locozodiac]

Sparky,

Good to read it worked near perfect for your setup. Just for the reccord, the splash was over or back transom ? If with aereation on close turns try different shim heights like 10 mm.

Check visually water flow height, must skim right under water deflector plate, with different minimum shim heights try to match that ideal settting.

Merc's are rebadged Tohatsus, that's why with splash issues too..

Happy Boating

[sparky666]

I'm a big fan of running a high engine, my old eurosport with a 90 2 stroke had the cav plate on top of the water and it was perfect
Bit it was a lot more stable and had a clean hull so cavitation was never a problem and it always got plenty of cooling water
The sib has a more unreliable underside that tends to mess the water up (all that air and turbulence )
Good compromise boat though

[Locozodiac]

You won't know the real performance difference if you have not tried it out, try a 10 mm shim and test same, unless you already have bolted that engine to transom. The ideea is to take the max HP out from portable engines and ligh sibs.

Happy Boating

[Projectile]

Hi Loco,

I understand what you're saying.

I asked you a clear and straight forward question in my last post in this thread. Do you know the answer?

[Fenlander]

>>>If you could instantly modify the transom height, which of the 3 lower leg heights (pic 2) would you choose for top boating, what kind of water performance would you expect to achieve with the chosen one ?


Re the question above here is your thread Locozodiac with lots of information.