Reply
 
Thread Tools Search this Thread
 
Old 18 August 2014, 15:18   #1
Member
 
Country: UK - England
Town: Bournemouth
Boat name: Colonel Mustard
Make: Hard nose!
Length: 5m +
Engine: 07 Yamaha 90 2-st
Join Date: May 2009
Posts: 15
Yamaha 90 cavitation - any advice on new Prop??

Hi all,
Can anyone suggest best way to figure out the right prop for my needs??

I recently picked up a hard nose 5.6m RIB with a big heavy old engine on the back (200...way bigger/older than I want!), and replaced it with a 2007 2-stroke Yam 90 (very light 3 cyl) with factory prop.
It has plenty of power for what I want, picks up on plane no problem and when trimmed up does 34 knots which is fine, but it cavitates big time when turning and going over waves.

The engine is very light, and with the heavy hard nose I think it is sitting too flat in the water, but I have also heard that the Yamaha 'triangle' K series propellers do not grip well anyway.

I want to keep the same speed, still be able to get a wakeboard up, but want to lose the cavitation... can anyone suggest a better prop to get and ideal pitch/diam?

I may need to put a jacking plate on and push it further back from the transom to get the weight further back.

Existing prop is a 13 1/4 x 17K white alu factory prop. Any help appreciated. Thanks.
Attached Thumbnails
Click image for larger version

Name:	photo.jpg
Views:	180
Size:	110.6 KB
ID:	98057  
__________________

__________________
GAW405 is offline   Reply With Quote
Old 18 August 2014, 16:32   #2
Member
 
Country: UK - England
Length: 3m +
Join Date: Sep 2008
Posts: 2,572
Just so you know... The ribnet possy doesn't believe this is an osprey...
They've been watching it on fleabay for sometime... So will be interesting to see what they make of it now it's in the hands of one of their own..

I know nowt about props. But pretty sure you need a rev counter to know what's happening. Revs at WOT I believe...

I'd also try dumping some sand bags at the stern to see if that shifts things...
__________________

__________________
ShinyShoe is offline   Reply With Quote
Old 18 August 2014, 17:11   #3
Member
 
Dan Gurney's Avatar
 
Country: UK - England
Town: Bingley, West Yorks
Boat name: Iolar
Make: Redbay
Length: 6m +
Engine: Suzuki DF140
Join Date: Sep 2012
Posts: 1,030
Hard to tell from that pic but possibly a little high? I've been told mines too low at about an inch below bottom of transom but have left it alone for fear of this sort of problem (others have complained about props letting go in turns after raising too much in search of extra speed). Can you lower it a hole or is the yolk sat on the top of the transom?
__________________
Dan Gurney is offline   Reply With Quote
Old 18 August 2014, 18:23   #4
RIBnet admin team
 
Nos4r2's Avatar
 
Country: UK - England
Town: The wilds of Wiltshire
Boat name: Dominator
Make: SR5.4
Length: 7m +
Engine: Yam 85
MMSI: 235055163
Join Date: Jul 2005
Posts: 12,840
RIBase
Welcome to Ribnet

Given size of boat, prop pitch, motor and speed achieved, the 17" on there is about the right pitch-it's the same figures as my 5.4 does with a 17" on the Yam. Something else isn't right. It might be worth changing it for a slightly lower (1 to 2") pitch stainless.

Be aware you're probably going to face an awful lot of questions about your boat though-it's been speculated on for a long time.
__________________
Need spares,consoles,consumables,hire,training or even a new boat?

Please click HERE and HERE and support our Trade Members.

Join up as a Trade member or Supporter HERE
Nos4r2 is offline   Reply With Quote
Old 18 August 2014, 18:24   #5
Member
 
Country: UK - England
Town: Down South
Make: Northcraft 5.8m 1999
Length: 5m +
Engine: 2012 Tohatsu MD90C
Join Date: Sep 2013
Posts: 181
We currently have a similar problem with our boat on hard turns it cavitates quite a bit.

My engine currently has a repaired stock prop and we are looking for a new replacement in the future.

And have been advised to look at 4 bladed props they have better acceleration and supposedly have less cavatation but if your trimmed up. I would look at trimming down as you go into a hard turn and then trimming out again.

But If I were you I would go with the previous answer and put some weight to the stern as this is a easy cheap thing to try and is easy to change if the weight needs adding or reducing. Sand bags work a treat just try to lash them down last thing you want is them shifting as you go hard over.

I have the opposite problem to you as my engine is too heavy having a 135 v6 in the back and mine still cavitates but sorted a lot of the problems by putting 80kg up in the bow in the form of sand bags.
__________________
Solent Bombard is offline   Reply With Quote
Old 19 August 2014, 08:35   #6
Member
 
Nick Hearne's Avatar
 
Country: UK - England
Town: Bucks
Boat name: Blue & Ding Dong
Make: Ribeye,SR4 & Bombard
Length: 6m +
Engine: 115,50 & 15Hp Yams
Join Date: Feb 2004
Posts: 3,246
As said you can not expect to trim up to the limit B4 she cavitates to then turn hard with it not cavitating! You will need to trim down B4 the turn
how Is your cavitation plate compared to the bottom of the hull?
Higher lower or the same?
__________________
Member of the Ribeye supporters club!!!
Member of Bombard 380 Aerotec club
Member of SR4 club
Nick Hearne is offline   Reply With Quote
Old 20 August 2014, 15:14   #7
Member
 
Country: UK - England
Town: Bournemouth
Boat name: Colonel Mustard
Make: Hard nose!
Length: 5m +
Engine: 07 Yamaha 90 2-st
Join Date: May 2009
Posts: 15
Hi all, thank you for your thoughts.
I will definitely be trying some weight in the stern to see how that works, but I think height wise it is pretty close with the cavitation plate sitting maybe 1" max from the bottom of the hull. I do also think the boat has a heavy bow, and judging by the way it rides weight in the back of an offset plate to get the engine aft may be the best answer.

I do trim down before turning, as I would expect it to cavitate when fully trimmed, but it does still cavitate when I wouldn't expect it to. It will seem fine then just start slipping, so I will see if I can try a different prop or two.
__________________
GAW405 is offline   Reply With Quote
Old 20 August 2014, 15:16   #8
Member
 
Country: UK - England
Town: Bournemouth
Boat name: Colonel Mustard
Make: Hard nose!
Length: 5m +
Engine: 07 Yamaha 90 2-st
Join Date: May 2009
Posts: 15
Quote:
Originally Posted by Clamchowder View Post
Hard to tell from that pic but possibly a little high? I've been told mines too low at about an inch below bottom of transom but have left it alone for fear of this sort of problem (others have complained about props letting go in turns after raising too much in search of extra speed). Can you lower it a hole or is the yolk sat on the top of the transom?
The yolk is sat right on the transom, but if I knew it was the problem I would be able to take it down a bit or offset it wit a plate.
Thanks.
__________________
GAW405 is offline   Reply With Quote
Old 20 August 2014, 15:25   #9
Member
 
Country: UK - England
Town: Bournemouth
Boat name: Colonel Mustard
Make: Hard nose!
Length: 5m +
Engine: 07 Yamaha 90 2-st
Join Date: May 2009
Posts: 15
Quote:
Originally Posted by ShinyShoe View Post
Just so you know... The ribnet possy doesn't believe this is an osprey...
They've been watching it on fleabay for sometime... So will be interesting to see what they make of it now it's in the hands of one of their own..

I know nowt about props. But pretty sure you need a rev counter to know what's happening. Revs at WOT I believe...

I'd also try dumping some sand bags at the stern to see if that shifts things...
I have seen some of the discussions/speculation since buying it.... I am also now not certain what it is now I know more about it. I am hoping to try and find out if anyone has ideas?! I was dubious when it was advertised but I picked it up quite cheap in the end (I think) and planned to change the engine from the start, but hadn't really considered much else about it (spontaneous buy, wife not exactly over the moon!). I'm not too worried about the speed 32 knots+ is fine but just hope to get it set up so it is a better ride and reduce cavitation.

I will def. try some sand bags in the back next time I use it, and notice the WOT revs but I seem to recall they are about 4800-5000 before I start trimming when it gets to about 5500 at full speed before it starts slipping in a straight line. The boat stays pretty flat at this point, I think the heavy bow means that trimming the engine doesn't lift the bow as much as on other boats I have had... it's not a great ride like that to be honest so hopefully some weight in the stern will help!!
__________________
GAW405 is offline   Reply With Quote
Old 20 August 2014, 15:29   #10
Member
 
Country: UK - England
Town: Bournemouth
Boat name: Colonel Mustard
Make: Hard nose!
Length: 5m +
Engine: 07 Yamaha 90 2-st
Join Date: May 2009
Posts: 15
Does anyone use the horizontal foils/fins that are bolted to the cavitation plate these days?? I haven't really seen them fitted to boats much, is that just because they don't look too good?!
__________________
GAW405 is offline   Reply With Quote
Old 20 August 2014, 15:36   #11
Member
 
Country: Finland
Town: Helsinki
Boat name: SR 5.4
Make: Avon
Length: 4m +
Engine: Toh1 3,5 Yam 90/2S
Join Date: Oct 2009
Posts: 919
How about a 5 inch manual jack plate style CMC-65 ? You get balance more to stern, you don't need to mod the transom and the "relative" height of the engine will be lower, propeller having "clearer" water.
__________________
fun on a boat is inversely proportional to size...sort of anyway
C-NUMB is offline   Reply With Quote
Old 20 August 2014, 17:23   #12
Member
 
Landlockedpirate's Avatar
 
Country: UK - England
Town: St Helens
Boat name: Wine Down
Make: Maxum
Length: 8m +
Engine: Inboard
Join Date: Apr 2012
Posts: 934
Fitting Doel Fins will lift the stern even more, not what you want if the boat is bow heavy anyway.
__________________
Landlockedpirate is offline   Reply With Quote
Old 21 August 2014, 13:55   #13
Member
 
Country: UK - England
Town: Bournemouth
Boat name: Colonel Mustard
Make: Hard nose!
Length: 5m +
Engine: 07 Yamaha 90 2-st
Join Date: May 2009
Posts: 15
Quote:
Originally Posted by Landlockedpirate View Post
Fitting Doel Fins will lift the stern even more, not what you want if the boat is bow heavy anyway.
Good point, I was thinking of them more to help the cavitation but agree they would lift the stern and definitely not what I want. Thanks.
__________________
GAW405 is offline   Reply With Quote
Old 21 August 2014, 13:56   #14
Member
 
Country: UK - England
Town: Bournemouth
Boat name: Colonel Mustard
Make: Hard nose!
Length: 5m +
Engine: 07 Yamaha 90 2-st
Join Date: May 2009
Posts: 15
Quote:
Originally Posted by C-NUMB View Post
How about a 5 inch manual jack plate style CMC-65 ? You get balance more to stern, you don't need to mod the transom and the "relative" height of the engine will be lower, propeller having "clearer" water.
That's the sort of thing I was thinking...
Are these available in UK, only seem to be able to find them in US? Any idea on price?
Thanks for your help
__________________
GAW405 is offline   Reply With Quote
Old 21 August 2014, 14:48   #15
Member
 
Country: Finland
Town: Helsinki
Boat name: SR 5.4
Make: Avon
Length: 4m +
Engine: Toh1 3,5 Yam 90/2S
Join Date: Oct 2009
Posts: 919
Quote:
Originally Posted by GAW405 View Post
That's the sort of thing I was thinking...
Are these available in UK, only seem to be able to find them in US? Any idea on price?
Thanks for your help
Try Boatmad, pretty sure you will find a used one at reasonable price. You can always sell it on ebay if it does not work. I think in Your case, there is a good chance it would help.

A new CMC-65 is over her about 350 eur, dont know the UK price but possible slightly cheaper.
__________________
fun on a boat is inversely proportional to size...sort of anyway
C-NUMB is offline   Reply With Quote
Old 22 August 2014, 02:31   #16
Member
 
Country: UK - England
Town: Bournemouth
Boat name: Colonel Mustard
Make: Hard nose!
Length: 5m +
Engine: 07 Yamaha 90 2-st
Join Date: May 2009
Posts: 15
Quote:
Originally Posted by C-NUMB View Post
Try Boatmad, pretty sure you will find a used one at reasonable price. You can always sell it on ebay if it does not work. I think in Your case, there is a good chance it would help.

A new CMC-65 is over her about 350 eur, dont know the UK price but possible slightly cheaper.
Good thinking, I will have a look on Boatmad. Cheers.
__________________
GAW405 is offline   Reply With Quote
Old 25 August 2014, 09:48   #17
Member
 
Country: USA
Town: Oakland CA
Length: 3m +
Join Date: Feb 2005
Posts: 6,653
Quote:
Originally Posted by Landlockedpirate View Post
Fitting Doel Fins will lift the stern even more, not what you want if the boat is bow heavy anyway.
they also isolate the surface of the water from the area around the prop, assuming your AV plate is at or below waterline while planning.

jky
__________________
jyasaki is offline   Reply With Quote
Old 26 August 2014, 03:30   #18
Member
 
Country: UK - Scotland
Boat name: Wildheart
Make: Humber/Delta Seasafe
Length: 5m +
Engine: Merc 60 Clamshell
MMSI: 235068449
Join Date: Apr 2007
Posts: 4,650
Quote:
Originally Posted by Nick Hearne View Post
As said you can not expect to trim up to the limit B4 she cavitates to then turn hard with it not cavitating! You will need to trim down B4 the turn

+1.

If I am cruising in a straight line in flat water I'll trim up to the max. In the lumpy stuff I'll have it down a bit. I will probably have to replace my trim motor brushes before I change the fuel filter! (and I do hope that is a joke - but it illustrates my point)


Quote:
Originally Posted by Nick Hearne View Post
how Is your cavitation plate compared to the bottom of the hull?
Higher lower or the same?
Try the trim first - the water popping out form behind your transom will rise as it moves aft (or the boat moves forward - at risk of getting all Einstein) - either way, the cav plate level with the bottom of the hull is just a starting point.

I would play with the trim first, rememberiing everything is a compromise - perfect setup for flat water all out speed is going to get non optimal in lumpy corners... Which is why you have remote trim.

To put this in perspective - I used to have to set my old manual tilt SR4 up depending on what I was doing & the sea state. Moved the pin between one of 3 holes depending what I was doing in what weather.
__________________

__________________
9D280 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




All times are GMT -5. The time now is 17:53.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2020, vBulletin Solutions, Inc.