Prop Question....
Printed From: The Fishing Website
Category: General Forums
Forum Name: The Outboard Clinic
Forum Description: Anything related to outboard maintenance here....
URL: https://www.fishing.net.nz/forum/forum_posts.asp?TID=54137
Printed Date: 06 Jul 2026 at 5:42am
Topic: Prop Question....
Posted By: tas-tackle
Subject: Prop Question....
Date Posted: 31 May 2010 at 12:16am
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My Yamaha F60 has a 11 3/8 x 12G prop on it which is rated for a 40hp Yamaha and I occasionally get cavitation.. Its a heavy plate 16ft tin boat and the engine pulls 5800 revs with a top speed of 33mph. This engine was not on this boat originally with this prop set up.. so was wondering if there would be any benefit to changing props.. and is so what recommendations.. ------------- http://postimage.org/" rel="nofollow">  http://www.tas-tackle.co.nz |
Replies:
Posted By: Catchelot
Date Posted: 31 May 2010 at 10:55am
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Silly question John, but the motor is not mounted on the transom too high by any chance? ------------- "The sea, once it casts its spell, holds one in its net of wonder forever." - Jacques Cousteau |
Posted By: Outboard Performance
Date Posted: 31 May 2010 at 12:30pm
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You also need to find out what the recommended maximum rev range is before even considering changing prop. |
Posted By: tas-tackle
Date Posted: 31 May 2010 at 1:33pm
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Al.. I installed the motor and put it in the same spot (read holes) as was the original Mariner 40.. Being the same length motor I presumed it would be the ideal spot.. Over the weekend I did a little home servicing/cleanup/polish and removed the prop to ensure no cracks or fishing line behind the prop.. Having looked up props on trademe, I find it is also for a 60hp motor... (289584902) Must check the rev range and also, look out the back of the boat once trimmed out and running to see where the cav plate is.. ------------- http://postimage.org/" rel="nofollow"> http://www.tas-tackle.co.nz |
Posted By: Unclejake
Date Posted: 31 May 2010 at 1:51pm
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Yamaha says that F60 motors should run between 5000 and 6000RPM at WOT so a 12P is about right for you.
You could try a 4 blade 12P to allow more trim adjustment without cavitation, fit a Dolfin/Permatrim, lower the motor a bolt hole - or put up with a bit of cavitation now and again.
It is also reassuring to hear that you get 33mph at 5,800. We get 28 knots at the same revs with a four blade 12P at WOT (which is 33 mph)
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Posted By: Outboard Performance
Date Posted: 31 May 2010 at 2:14pm
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As Unclejake said, if thats the rev range, the prop is all good for you. If you never water ski or load the hell out of the boat you could go up a size in pitch. Remembering the bigger pitch the less accelleration. Also can fall off the plane easier when travelling in rouch following sea. Adjust the jockey wheel on trailer to get bottom of boat parrellel to ground. Then trim motor to get parrellel with ground.
Run a straight edge or level or something along the 'v' of the hull and see where it hits the leg.
The cav plate should be around 1/2 inch above the v. - up to 3/4
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Posted By: tas-tackle
Date Posted: 31 May 2010 at 5:46pm
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Cheers OB... will have a nosey.. measure up... unclejake..its a 12G .. 3 blade... if that makes any diff...
------------- http://postimage.org/" rel="nofollow"> http://www.tas-tackle.co.nz |
Posted By: Unclejake
Date Posted: 31 May 2010 at 5:47pm
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Nah. Same thing AFAIK
When I say 12P I mean P for pitch. 12 = 12" of theoretical forward movement for every revolution of the prop
G in your case is the G Series of prop (to suit 40-60HP probably)
EDIT: Oh, FYI we tried a 14P and could not get the boat to rev over 4,800RPM. Top speed was pretty similar though @ 1-2 knots slower than with the 12P
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Posted By: Catchelot
Date Posted: 31 May 2010 at 6:01pm
What happens if the cav plate is below the Vee OB? ------------- "The sea, once it casts its spell, holds one in its net of wonder forever." - Jacques Cousteau |
Outboard Performance wrote:Posted By: Unclejake
Date Posted: 31 May 2010 at 6:24pm
| ^ In my very limited experience the top speed performance will be reduced and the boat may porpoise |
Posted By: Outboard Performance
Date Posted: 31 May 2010 at 8:48pm
| If the cav plate is bellow catchelot it will be a poor performer. As unclejake said it will loose top end speed, the fuel economy will be poor. the steering will be heavier. And it can also do damage to the engine because it can kick up too much salt spray and then the motor can draw it in. If you have a really salty powerhead and no transducer on the boat it can be a cause of that. |
Posted By: Seadoc
Date Posted: 01 Jun 2010 at 9:09am
| "Fisher", I have the same engine on a 4.7 Surtees and have a 13P prop, giving me about 30knots and 5800rpm at WOT with 2 POB. I have done quite a bit of asking around and reading up and have ordered a 13P Solas SS prop. I would definitely not lower the engine if I occasionally get "cavitation" (it is actually "ventilation") but rather go for a SS prop of the same pitch which should stop the ventilation problem and give you a little bit added performance due to the increased stiffness and thinner blades of the SS. I recently lifted my engine 1 hole and the increase in performance both out of the hole and top speed was noticeable. I will give some feedback once I have fitted the SS prop. They do not have any 13P in stock because the Thundercat boys cleaned them out! |
Posted By: Unclejake
Date Posted: 01 Jun 2010 at 11:46am
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BTW - the 50hp Mercury props fit the Yamaha F60
Seadoc - I would still be interested in your alloy F60 13P if you are not keeping it. I have a new F60 14P I don't want if it is any interest to anyone else. The best result would be a straight swap for a 13P
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Posted By: Seadoc
Date Posted: 01 Jun 2010 at 1:21pm
| I will let you know when I get the new one, Unclejake! Mine is not as shiny as yours though! |
Posted By: Unclejake
Date Posted: 01 Jun 2010 at 6:55pm
| Thanks Seadoc. Let us know whenever you decide what to do. |
Posted By: tas-tackle
Date Posted: 01 Jun 2010 at 10:24pm
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Cheers Seadoc... saw your boat in Mangonui when you were up... I need to go look see at where I have the engine mounted and check the hull to Cav plate... Next time I'm out, I will find a bit of ripple water, trim it out on the fuel computer and see what sort of revs and speed it pulls at WOT and check the Cav plate to see how its running out the back... Be interesting to see what, if any difference the change in prop does to your boat Seadoc ... ------------- http://postimage.org/" rel="nofollow"> http://www.tas-tackle.co.nz |
Posted By: Unclejake
Date Posted: 02 Jun 2010 at 12:30am
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If you don't mind publishing your findings wrt trim and revs I would be very interested. We do not pick up revs with the motor trimed out and perhaps that means our motor is too low?
We have our motor on a pod so the maths is a bit different
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Posted By: Seadoc
Date Posted: 02 Jun 2010 at 10:41am
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Unclejake, my boat is quite sensitive to the trim, I can easily pick up 200rpm when trimmed correctly. I always trim my boat to the conditions - in when getting on to the plane, then trim out until I just start getting a little ventilation and then a bit in again. If i am about to make a fairly tight turn I trim it in again. Being a centre console it also keeps the crew dry if the nose is up! I will report back once I have the SS prop
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Posted By: Unclejake
Date Posted: 08 Jul 2010 at 2:19pm
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Just an observation for fun: Normally we see about 20 knots @ 4,700rpm but on Sunday we had nine PoB (yes, 9) and at 4,700 rpm we were doing 13/14 knots.
I hadn't realised just how much these props can slip under load
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