Prop Size, 90hp Mercury 4stroke on 5.85 Ribcraft

[JABS]

Hi,

Can anyone give me some advice on which would be the best prop size for a Mercury 90hp four stroke on a Ribcraft 585? I want to buy a new prop and keep the old one as a spare and can't read the size.

Is it worth the extra for a stainless prop, given that I do use the boat in difficult harbours in Norfolk, hence the risk of grounding.

Thanks!

[three-rex]

Hi this might be useful: mercury prop selector
http://appcenter.mercurymarine.com/propSelector/

They seem to suggest 25 or 26 pitch

[Jono Garton]

Originally Posted by three-rex

They seem to suggest 25 or 26 pitch

I bet it would only get 2500rpm with a 25 or 26, should be revving to 5500 - 6000

I would guess a 17 pitch ally or 18 pitch stainless, best to confirm with Jason @ Ribcraft or hve a look at Jools site www.ribpanther.co.uk (ribcraft with 90hp merc 4 stroke)

Drop Ian a line on 07947807349 and he will get you a new prop cheeper than anyone else, hes got loads of props for merc/mariner in stock.

Jono

[Pete7]

Originally Posted by three-rex

They seem to suggest 25 or 26 pitch

I would have thought 17" or 19" near the mark. Size is stamped on the end of the prop with the part number, but if you can't read it send it to Steel Developments and ask them to measure it. They should be competitive in quoting a replacement prop too.

Pete

[three-rex]

Originally Posted by Jono Garton

I would guess a 17 pitch ally or 18 pitch stainless,
Jono

Is what I thought - I was just saying what the calculator said - must have been using a different gear box on the calculator model

Odd - I just done it again and it suggests 19 - 20 - just as I suspected - I'm shite!!!!

[Nick Hearne]

My old 5.75 Viper with a 100hp 2st ran with a 19 when lightly loaded & a 15 when up to 8 divers & kit!

[JABS]

Looks as if I need to go for an 18!

Anyone tell me whether to go for stainless or ally?

Thank you!

[BogMonster]

Originally Posted by JABS

Looks as if I need to go for an 18!

Anyone tell me whether to go for stainless or ally?

Thank you!

when I looked into this the best answer seemed to be stainless for best performance if you don't expect to hit anything, alli if you are operating/launching in conditions where you might whack the prop on the bottom because if you do this with an alli prop it will break the prop, if you do it with a stainless it will (might) break the gearbox instead

so as I launch off a rocky beach I bought an alli, and I have belted it on the bottom already so glad I chose what I did

[Cabs]

Originally Posted by JABS

Looks as if I need to go for an 18!

Anyone tell me whether to go for stainless or ally?

Thank you!

I'd agree with Stephen... stainless is great for top end performance, but if you're going to in and around the rocky shore - definitely stay with aluminum. Better to have a sacrificial prop than a sacrificial lower unit. Take a look at the Ribcraft USA RIB Blog. They've been talking about props lately. www.ribcraftusa.com/blog