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Old 28 March 2004, 02:36   #1
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Country: UK - Scotland
Town: Greenock area
Boat name: Joni Chimpo
Make: Narwhall
Length: 4m +
Engine: 50hp Mariner
Join Date: Mar 2004
Posts: 131
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Newbie and a quick question

Hey folks a newbie here so be gentle....

Just bout a 4.5m Narhwall on Friday with a 1994 50hp Mariner.

I've been told that the performance and speed of the boat is greatly adjusted depending on the prop thats used. Is this correct and if so what would be the correct size and pitch of prop for this boat and engine?

Thanks in advance...
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Old 28 March 2004, 04:42   #2
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Country: UK - England
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Boat name: Tigger II
Make: Bombardier Aerodeck
Length: 3m +
Engine: Tohatsu 25HP
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Hi Gary

& welcome to RIBnet

Well your right in part but as with all things its not that stright forward. If you do a search on "props" you will find many many posts of people trying to find the right prop.

Anyway to get you going on a 50HP things get a little more simple.

To startwith you may as well stick with alloy props, the peformance stainless ones dont give you much extra on a 50HP.

the next question is how will the boat run with respect to weight
If its going to be heavy loaded a smaller pitch prop will get you on the plane quicker but at the expense of top end speed, a high pitch one the opposite.

As you can see its all a compromise, but you should aim to be not overrevving when light loaded and WOT.

On my previous Ribcraft 4.* I ran a 15" pitch (I think) on a Mariner 50HP 4 Stroke.

The other option is to go for a composite prop such as Pirahana which the can change ther pitch on (not while moving)

Anyway do a search, their is a bit above.

Have fun

Regards Gary
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Old 29 March 2004, 05:56   #3
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Country: UK - Scotland
Town: Greenock area
Boat name: Joni Chimpo
Make: Narwhall
Length: 4m +
Engine: 50hp Mariner
Join Date: Mar 2004
Posts: 131
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Thanks for the help Gary, I will do a bit of digging about and see what I can find....
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Old 29 March 2004, 06:26   #4
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propeller selection

The choice of propeller will depend on how you want to use the boat, and the weight it would carry for the majority of the time, i.e. the number of people. Basically the lower the pitch the greater the acceleration or the more weight it can carry and still be able to plane. The higher the pitch the faster it will go but it will take longer to get on the plane in the first place. I would either recommend an aluminium prop or a stainless steel one. The s/s is more expensive but should give better performance. I would steer away from composite propellers as they generally give less performance and are more expensive to repair in the long run if you damage it as a single blade replacement is about 20-30+VAT whereas you can have an aluminium prop repaired (all blades) for 31.50+VAT. As a beginner I would recommend that it would probably be best for you to start with an aluminium prop and maybe upgrade to a s/s one later. Which ever you chose keep the prop in good condition as any damage to it will affect performance.

Hope the purchase goes well and welcome to ribnet
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