Fastroller 360 ventilation problem

[js232]

Just got myself a new Zodiac FR360.
I run a yamaha two stroke 15hp short shaft with a brand new 10-1/2P yamaha prop.
No probs getting on plane with a good load.
I tried the boat in light chop. 6-12 inch wakes. Boy does that boat bring air to the prop. I mean, it makes the boat less than enjoyable! I can’t even keep the boat to a constant speed (15-20 mph) without experiencing ventilation to a point that I have to quickly cut down the power. I will blow my engine if not being cautious.
Is this a known problem for that model boat? I tried a friend’s yamaha 8hp as well: same problem!

is there a way to get around this? Someone told me to use a piece of wood to raise the motor on the transom? I feel it would get worst...

Hydrofoil? If so, Stingray junior or
Se sport 200?

Any help appreciated

[Fenlander]

I've owned two of this 360 model plus two of the smaller 340s with the same floor.

The basic fact is that a flat air floor SIB with low pressure sausage keel or high pressure linked keel is more prone to this than an alloy or V-air floor model... and the longer the SIB the worse the problem.

It can be quite specific to your own setup... outboard type and even prop. Plus of course your loading and water type you operate in.

Some folks never seem to experience it (or never tell!) and others it drives them to change the SIB.

My own experience with the 360 correctly inflated (very important, floor in particular)... powered with a Mariner 15hp 2-stroke and evenly loaded was hardly ever seeing the problem but now and again for no reason it would happen.

One particular occurance was interesting though. I bought a spare prop for the Mariner which was a Solas and had much broader petal shaped blades than the original swept style ones. This produced the most dreadful ventilation so I replaced it with a genuine type and all was OK.

[SixtyNorth]

It would be worth checking that the floor and tubes really are inflated to the correct pressure once the boat is in the (cooler) water. Next I would experiment with the loading... weight distribution.

[js232]

Would a hydrofoil help?
Also I measured tonight and the cavitation plate of the yamy is almost 2-1/2 lower than the bottom.
I read everywhere that it should be between flush and 1 inch

[Fenlander]

I'm no fan of hydrofoils as they just add drag and sometimes odd handling... but have to admit sometimes when nothing else works in changing your setup, engine height or trim then they could just be an answer.

Re the outboard depth well yes to many here including myself the AV plate (cavitation) level or 1" below hull bottom at transom is the starting point and often ends up being the right level. But if you are already suffering ventilating when a bit deep raising could cause more of the issue... but air floors do not behave by the rule book so I'd try it raised with a packer to see what difference it makes. I'd be trying at least an inch raise or a bit more if the outboard clamps allow.

Image attached of my 360 and Mariner 15 2-stroke below... just for interest. I didn't use any packer with that setup because despite being a bit low (perhaps 2" under the hull) it had good speed and no splash.

Video of it below too. I had just one passenger and when I straighten up around 36sec I take it to maximum speed and you'll hear there is no slip. Speed towards the end would have been about 23mph (20kts).

The slip was rarely noticed with a minimal load... nearly always when 4-up which makes sense as the prop is looking for more grip to push the load.

So for you I'd try... make 100% sure it is up to pressure once it's been in the water a few minutes as SixtyNorth advises and ensure you are happy the gauge you are using is accurate... ensure the outboard trim is set midpoint... ensure your passenger load brings the boat as level as possible... try a packer to lift the outboard 1-1.5"... try with just one passenger and see if the problem is the same... consider pitching the prop down to a 9" which is what my Mariner was fitted with... and then finally possibly a hydrofoil.

https://www.youtube.com/watch?v=6FO00b88Oj4

[Fenlander]

This video is interesting because if you listen and watch carefully around 30sec the engine note changes and it flicks for a split second as if it's hit something... that was the infrequent ventilation slip we'd get.

But when I put the prop on that didn't suit it that jerking and slip happened most of the time if we tried to go above about 15mph... so very much like your problem.

https://www.youtube.com/watch?v=P8aIvzwGyAo

[jeffstevens763@g]

the last vid looks interesting it might be my eyes but if you look at the rubbing strake it seems to bow up with the peek about where the middle passenger is making it look banana shaped.

[Fenlander]

Yes good spot Jeff. At rest the boat is basically level and in shape but as you get up on the plane the flat air floor design is unable to resists the forces of the weight distribution and water flow so it twists out of shape.

[jeffstevens763@g]

Originally Posted by Fenlander

Yes good spot Jeff. At rest the boat is basically level and in shape but as you get up on the plane the flat air floor design is unable to resists the forces of the weight distribution and water flow so it twists out of shape.

yep soon as the power goes on it bends um not a good design IMO

[js232]

I remember reading somewhere someone posting about adding a wooden slot under His fastroller’s floor. I can’t find it. I wonder how He did it and what kind of improvement He got

[billows]

How does motor trim affect ventilation? I experience it now and then on the Honwave in a chop.Very disconcerting when the engine revs up and no drive

[js232]

Tryed to lift the outboard with a piece of hockey stick. About an inch. It help ALOT!
Still... that floor wobles a lot under load...

Fenlander, the specs are for 6 passengers on that boat. I don’t understand Zodiac for this.
I guess the only way to get around this would be to insert some plywood or pvc plank under the air floor to add strength.