air bubble under the floor and cavitation on the prop

[slate1234]

I got my boat in the water today it's a 3.2m v air floor and 9.8hp tohatsu, all was great upto about 10mph the I get cavitation on the prop and a large bubble under the floor just in fron of the transom any helpwould be welcome

 

[ronaldj]

Re: air bubble under the floor and cavitation on the prop

2 questions
Is your air floor a high pressue air floor
Do you have a high pressue electric pump?

No matter what the mfg tell you , you have to have a high pressure electric pump to properly inflate the air floor.
You also need a pressure gage.
If the floor is improperly inflated or you use a long shaft engine.
You will experience what you described

 

[Sea Rider]

Re: air bubble under the floor and cavitation on the prop

Although air V floor is infalted, it's severeley under inflated to perform satisfactorily. That V air floor needs 12 to 14 psi to perform well along tubes inflated to a 3.0 psi minimum to achieve overall sib rigidity. Get an electric inflator with gauge or if on tight budget a Bravo alu 4 hand pump with gauge.

Happy Boating

 

[slate1234]

Re: air bubble under the floor and cavitation on the prop

Thanks for the replys, I tried again today with the same results I am pumping the tubes to 0.25 and floor to 0.35 useing this gauge I use the inner red part, is this correct ?? the boat gets on the plane easey with two of us in but the bulge in the floor is causeing a lot of ventilation/ cavitation (prop seems to be in and out of the water)

 

[slate1234]

Re: air bubble under the floor and cavitation on the prop

sorry yes it is a high pressure floor and no I dont have a pump I use a compresser I use the gauge as above

 

[ronaldj]

Re: air bubble under the floor and cavitation on the prop

You need to fill it to the Black 12

You should really get a dedicated high pressure pump

 

[Sea Rider]

Re: air bubble under the floor and cavitation on the prop

Test sib again on flat calm no wind waters and inflate both keels to minimum 0.8 bar or 12 psi and tubes to min 3.0 psi or 0.2 bar. Check if water performance bettered compared to previous defleted run. What's the bar/psi factory recommended working pressure for that V deep keel ? Bear in mind that as soon you place that sib on water, worst if being cold, pumped pressure will drop accordingly, if you have a hand gauge check, probably will need to top 1-2 psi more to compensate pressure loss once on water to maintain 12 psi.

All flat air decks, V deep keels seems not to hold high pressure which were inflated to for long time periods, are prone to experience environmental pressure loss quite fast, much worst throughout the boating day. Tohatsu horses are prone to experiment back transom issues if not properly transom seated, tail design issues. Probably will need a engine/transom match optimization for prop thrust maximization...

Happy Boating

 

[slate1234]

Re: air bubble under the floor and cavitation on the prop

Thank's again for the replys, the plate on the transom is saying 0.25 bar for the tubes and 0.35 for the keels the plate is worn and I'm woundering if the 3 is a 8 ??

 

[ronaldj]

Re: air bubble under the floor and cavitation on the prop

Who made your boat?
Air Floors and V Hulls are almost always High Pressure.
is it possible that this floor was addded at a later date than the original floor?

 

[Sea Rider]

Re: air bubble under the floor and cavitation on the prop

Issues to consider :

If yours is a deep V keel hull made out of thousands of crissed-crossed fibers with just 0.35 bar will have a very underinflated and poor perforrmer hull, lacks rigidity. Should be on its own right inflated to 0.85 Bar which is around 12.5 psi. Inflate to that pressure and test again.

Happy Boating

 

[slate1234]

Re: air bubble under the floor and cavitation on the prop

yes it is the deep V hull, and the ad says thousands of crissed-crossed fibers, I will inflate to the above pressure at the weekend and report back
Thanks slate