Reply
 
Thread Tools Search this Thread
 
Old 31 August 2001, 00:18   #1
Member
 
Country: Mexico
Town: Chihuahua, Mexico
Make: Seaeagle
Length: 3.8
Engine: Outboard, gasoline, 15HP
Join Date: Aug 2001
Posts: 3
cavitation problem

Hi to all, and thanks to batfalcon for inviting me into this forum.

I have a 12.6 inflatable (not a RIB) powered by a 15hp mercury, used mainly in freshwater reservoirs for bass fishing. The problem I have is that more often than not, the motor will start cavitating. I think it may be due to the rounded tubes it has (instead of the usual cone shaped ones) and that at the manfucaturerīs suggestion I got a short shaft OB. Cavitation will usually start after a couple of seconds while gaining speed, but is seldom (or never) a problem once the boat is running at the top speed allowed by the outboard.

I was wondering if it would help to bolt to the anticavitation plate one of those plastic extensions. I would really hate to drill the plate if this will not help or prove more damaging at the end.

Thank you all for your input on this matter.

P.S. This is my first time really using this forum, so please be patient with me as Iīm not familiar with the siteīs format.
__________________

__________________
Saludos,

Omar
Omar Hernandez is offline   Reply With Quote
Old 31 August 2001, 01:55   #2
Member
 
Country: UK - Scotland
Town: Highlands
Boat name: Quicksilver
Make: Quicksilver
Length: 3m +
Engine: Mariner 15hp
Join Date: Aug 2001
Posts: 1,771
Hi

This sounds like a simmilar boat to mine. Excuse the ignorance of a newcommer, but, what is cavitating?

Keith Hart
__________________

__________________
Keith Hart is offline   Reply With Quote
Old 31 August 2001, 02:28   #3
Member
 
Country: Greece
Town: ATHENS
Boat name: SUN KISS II
Make: Nuova Bat 9 Falcon -
Length: 5m +
Engine: Outboard Mercury 115
Join Date: Jun 2001
Posts: 639
Send a message via Skype™ to batfalcon
Cavitation

Due to extreme water pressure on the front surface of the prop's blades, water tends to boil, thus creating millions of bubbles. In other words a film of air between the prop's metal and the water. The prop looses the contact with the water thus thrust is beiing reduced and the rpm increased to the limit. Of all the above can be fasten up by the wrong installation height of the engine on the transom. That's all in a few words.

Michael
__________________
batfalcon is offline   Reply With Quote
Old 31 August 2001, 03:52   #4
Administrator
 
John Kennett's Avatar
 
Country: UK - England
Town: Brighton
Length: 3m +
Join Date: May 2000
Posts: 6,830
My guss is that it is more likely to be ventilation rather than cavitation. There's a selection of articles about it here

Is there any damage to the "hull" fabric, especially around the transom? This can cause this problem with inflatables.

Unless the boat is a weird design, then a short shaft outboard is likely to be correct. The bolt on hydrofoils may help, but there's no guarantee! They do seem to to be more effective on smaller, low performance boats like yours though.

John
__________________
John Kennett is offline   Reply With Quote
Old 31 August 2001, 04:13   #5
Member
 
Country: Greece
Town: ATHENS
Boat name: SUN KISS II
Make: Nuova Bat 9 Falcon -
Length: 5m +
Engine: Outboard Mercury 115
Join Date: Jun 2001
Posts: 639
Send a message via Skype™ to batfalcon
John,

Thanks for the correction AND for the list of articles. Whatever is called (cavitation or ventillation) it can't do any damage to the soft hull's fabric, because all these things happen behind the transom , away from it and UNDER the water's surface.

Michael
__________________
batfalcon is offline   Reply With Quote
Old 31 August 2001, 04:40   #6
Administrator
 
John Kennett's Avatar
 
Country: UK - England
Town: Brighton
Length: 3m +
Join Date: May 2000
Posts: 6,830
Sorry, I don't think I made myself very clear!

What I meant was damage to the bottom of the boat, especially at the transom, can cause ventilation at the prop as the water flow is disrupted.

I had a similar problem with a 4 metre inflatable a few years ago after a previous owner had run the boat onto the beach and then done a dodgy repair. Thinking about it though, this was more of a problem at high speeds once the boat was on the plane . . .



John
__________________
John Kennett is offline   Reply With Quote
Old 31 August 2001, 07:07   #7
Member
 
Country: Greece
Town: ATHENS
Boat name: SUN KISS II
Make: Nuova Bat 9 Falcon -
Length: 5m +
Engine: Outboard Mercury 115
Join Date: Jun 2001
Posts: 639
Send a message via Skype™ to batfalcon
Misunderstanding

My fault, sorry

Michael
__________________
batfalcon is offline   Reply With Quote
Old 31 August 2001, 11:32   #8
Member
 
Country: UK - Scotland
Town: Highlands
Boat name: Quicksilver
Make: Quicksilver
Length: 3m +
Engine: Mariner 15hp
Join Date: Aug 2001
Posts: 1,771
My little inflatable has a short shaft engine and it was the one recommended by the manufacturer (in fact I think they are both from the same company Quicksilver and Mariner), I don't recall having any problems like this so short shaft must be the answer.

Keith Hart
(1 more post towards my Senior Membership)
__________________
Keith Hart is offline   Reply With Quote
Old 31 August 2001, 14:36   #9
Member
 
Country: Other
Make: FB 55
Length: 10m +
Join Date: May 2001
Posts: 1,711
Prop

What prop are you using?
__________________
Charles is offline   Reply With Quote
Old 01 September 2001, 02:12   #10
Member
 
Country: UK - Scotland
Town: Highlands
Boat name: Quicksilver
Make: Quicksilver
Length: 3m +
Engine: Mariner 15hp
Join Date: Aug 2001
Posts: 1,771
Re: Prop

Quote:
Originally posted by Stealth
What prop are you using?
Good morning. Who's prop are you asking about?

Keith Hart
__________________

__________________
Keith Hart is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off





Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -5. The time now is 08:22.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.