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Old 22 May 2010, 11:36   #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, 17:15   #2
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You need a bigger engine!
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Old 23 May 2010, 02:42   #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, 03:36   #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, 04:01   #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, 04:05   #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, 04:07   #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, 08:50   #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, 03:48   #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, 12:34   #10
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You really want that much weight going through your AV plate?
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Old 24 May 2010, 13:10   #11
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hmmmm
not the slightest idea in this, but that is what they said would do it.

remember, my boat very nearly planes, in fact, with the wind in the right direction, she will plane. but you are waiting for a bit of wind, or a wave to get here there, then she is fine.

i presume that they can take it in the av plate or you would hear of stories where there is faliure there because of them???

can you elaborate your concerns?
thanks
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Old 24 May 2010, 14:01   #12
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hmmmm
not the slightest idea in this, but that is what they said would do it.

remember, my boat very nearly planes, in fact, with the wind in the right direction, she will plane. but you are waiting for a bit of wind, or a wave to get here there, then she is fine.

i presume that they can take it in the av plate or you would hear of stories where there is faliure there because of them???

can you elaborate your concerns?
thanks
Probably, but I wouldn't really want to be drilling holes in my AV plate and fitting doelfins when a prop change will do the job anyway and is easy to reverse when you want to use the boat solo..

I don't like the bloody things anyhow, they can cause some very odd handling at speed.
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Old 24 May 2010, 14:09   #13
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yup. i thought i could smell marmite!
LOL!
i do know they are love 'em or hate 'em and wondered if that was your camp.

i talked at length with the guys at steel d. and they took the details of the boat, engine and so on.
i did say about a prop change and the sizes you said.

they said it would work as you say, but risks over reving the engine. not a problem if i am at the helm, but if someone else uses the boat, and forgets, the damage would be awful.

he was sure the hydrofoils would do the trick, and at £30 a cheap fix. compared with a prop.

prop is plan B if the hydros dont work.
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Old 24 May 2010, 14:23   #14
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yup. i thought i could smell marmite!
LOL!
i do know they are love 'em or hate 'em and wondered if that was your camp.

i talked at length with the guys at steel d. and they took the details of the boat, engine and so on.
i did say about a prop change and the sizes you said.

they said it would work as you say, but risks over reving the engine. not a problem if i am at the helm, but if someone else uses the boat, and forgets, the damage would be awful.

he was sure the hydrofoils would do the trick, and at £30 a cheap fix. compared with a prop.

prop is plan B if the hydros dont work.
I had a set cause uncontrollable veering off from side to side on a boat once. Never again.

Be careful the first time you take it out solo with them on.
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Old 24 May 2010, 14:25   #15
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will do, your advice is much appreciated

i will be careful.

i did have them on my last boat/engine.
never had a problem,
but i take on board your concerns

thanks
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Old 31 May 2010, 14:25   #16
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ok, so as promised i said i would report back on the Doel Fins

result:

it worked!
i got up on to the plane, fully loaded, with ease.

she was stable, she went in circles well, and all was fine.
top end was 30mph, so i was happy with that
wot revs 5000rpm

so i know the doel fins are 'marmite'

but they have worked for me!

very happy!

thanks again for the advice, much appreciated
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