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Old 22 May 2010, 12:36   #1
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which prop do you think i need?

hi all

i have a yam 90hp

when on my boat, and fully laden with divers, the boat struggles to get on the plain
when there, she flys!
she weighs about 1.5tonnes laden,

currently she has a 13 1/2 x 15-k prop
today, with the rev counter, she was doing 3500-3800 revs only
she was doing 10knotts

so which prop would give me the extra kick i need, but not too much that i would risk overreving the engine when on the plain?

thanks for any help
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Old 22 May 2010, 18:15   #2
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You need a bigger engine!
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Old 23 May 2010, 03:42   #3
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that option occured to me, LOL!
but its not a good plan at present
she very nearly gets on the plane, and sometimes she does, and hey presto, i get 30knotts then. its just not quite there
i am thinking a prop change may sort it

hence the thought about the prop. seeing i have several K of revs free.

what about foils?

any other ideas - apart from chucking a diver overboard!
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Old 23 May 2010, 04:36   #4
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You could try dropping to a 13" pitch 4 blade prop. It would give you more oomfff onto the plane, but you will loose out on top speed. Also worth ringing steeldevelopments for advice. They relly know their props
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Old 23 May 2010, 05:01   #5
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You could try dropping to a 13" pitch 4 blade prop. It would give you more oomfff onto the plane, but you will loose out on top speed. Also worth ringing steeldevelopments for advice. They relly know their props
I reckon you're right.
I'd be tempted to drop to a 12" pitch as well in a 4 blade though.
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Old 23 May 2010, 05:05   #6
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I reckon you're right.
I'd be tempted to drop to a 12" pitch as well in a 4 blade though.
That'll get you out of the hole, but you mightn't see 30knts again. More gee gees are what's required.
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Old 23 May 2010, 05:07   #7
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That'll get you out of the hole, but you mightn't see 30knts again. More gee gees are what's required.
Apparently it's on it's max rated HP now. I wonder if it's overloaded.
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Old 23 May 2010, 09:50   #8
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not overloaded, it was rated for 8, but its past life ment it was built full of heavy metalwork

its fine normally, fishing and so on, but when we get out to dive, then she struggles.
all the extra weight just makes it hard for her.

thanks for all teh advice, i will call the guys you mention, and start to look for a prop.

any links to the right prop???
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Old 24 May 2010, 04:48   #9
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spoke to steel developments
he says no to a prop change, but fit hydrofoils
if they dont work, then a 13inch prop

so, hydrofoils first, and then see from there

he was concerned that a drop in prop size would risk engine overrevving

so i will try his plan first


thanks for all the advice, i will post up what happens!
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Old 24 May 2010, 13:34   #10
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You really want that much weight going through your AV plate?
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