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Old 01 December 2004, 06:34   #21
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Quote:
Originally Posted by swginn
Dan,

Was talkin to my Merc engineer today, while booking the Opti in for her service. I explained your situation to him. He said that something didn't sound right and that it sounds like your engine was set-up too high and to bring it in and he'll sort it for you. (Then I explained where you were!!) They've set up plenty of Ribcrafts, Zodiacs and Valiants with Merc 40/50/60 2strks and have never needed to change the prop from the standard alu one.

Fair enough the stainless prop may sort all your problems, but it also might not. I personally would like to have the engine set up right first before I went tinkering about with props. The temptation is there to get a nice shiney stainless one, but this may not be the answer.
i had the engine set up checked when it was service they said its in the right place and i can,t lower it with out cutting the transom its sitting hard on the lip at the mo my old valiant v450 would slip in turns but not as bad as the new one i can only think that upgrading from the recomended 40hp to a 50hp
on my new boat as made the problem worst ??

richard

yes i do agree i need to try the rib with the new trim tab fitted as this may
play a big part but most have said that a trim tab will not affect the cavetation in turns but i don,t agree i think it may improve the problem as my last rib did it i do think that its some thing that a ss prop will sort out but not
get rid of completely and i will have to live with some slip


dan
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Old 01 December 2004, 06:58   #22
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Dan

At the end of the day its your money of course, the anode missing will have some effect on the set up, at the moment you have a big hole under the cav plate thats sucking air down through the bolt hole in the leg, this cant be helping much.

I'd replace the anode and see if it makes any difference and then re asses from there, you have to replace the anode anyway so why not wait and see if it makes any difference, dispite what all the experts on here think a stainless prop the same size as you have on now will make no difference to your boats performance at your size engine, if you increase the pitch then you start to mess about with the dynamics and handling of the boat and as you have no room to lower the engine increasing pitch might cause even more problems, 300 ish give or take for a stainless prop would buy you a nice VHF fixed set, a couple of base map cartridges, a good dry suit for wet weather cruises or even an RYA level 2 course, you could even treat Kel and the girls to a weekend away for that amount.
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Old 01 December 2004, 07:05   #23
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richard

are out this weekend i have a day pass

i have fitted the trim tab to so its worth a try

dan
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Old 01 December 2004, 07:36   #24
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Hope the trim tab improves things for you Dan, but remember not to over rev that engine!! IMHO I think you need to get those revs down and a prop is the only way you'll be able to do it if you can't drop the engine.

Have a read off Paul Lemmer's article on setting up your engine, it may shed some light on the issue.

http://www.ribmagazine.com/articles/...icaladvice.htm

Also it may not be a bad idea to contact Valiant. As a branch of the Brunswick Corporation I understand they only fit Mercury/Mariner engines on new boats, so surely they have come across this problem before.
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Old 01 December 2004, 09:28   #25
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Quote:
Originally Posted by swginn
Dan,

Also the change from Alu to Stainless should drop your revs even more because of the added weight (I am not sure on this one so maybe somebody else who has gone from alu to stainless can advise!!)
Other way round I thought. SS blades are thinner and more efficient hence higher RPM.
Going from a 19" Al to a 20" SS didn't change the maximum RPM.

I still reckon that the best / most cost effective option is to investigate with one or more secondhand propellers - that way if it / they don't work you can sell them on for almost as much as you paid.

Shelling out over 200 300 on a prop that might work may not prove good value - especially when you might struggle to get 150 for it secondhand?
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Old 01 December 2004, 10:10   #26
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spoke to

http://www.steeldevelopments.co.uk


and they can repair my old prop as it as a chip on and they think it could be
damaged and they will change the pitch to 14 for 35 quid sounds good to me
to check that its works before i change to ss steel


dan
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Old 01 December 2004, 10:24   #27
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Searider is correct, stainless steel does not flex like ali therefore does not need to be as thick, rule of thumb is that if you increase pitch up your'll lose 200 rpm for every 2" pitch increase, so its interesting that Searider increased 1" and noticed no difference in rpm ?
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Old 03 January 2005, 08:33   #28
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Quote:
Originally Posted by Daniel TD5
spoke to

http://www.steeldevelopments.co.uk


and they can repair my old prop as it as a chip on and they think it could be
damaged and they will change the pitch to 14 for 35 quid sounds good to me
to check that its works before i change to ss steel


dan
just a quick up date

had the prop repaired and fitted the anode trim tab have been out and the handling as improved the revs have droped by about 200rpm at full
speed the top speed as droped by about 1 knot

the prop does slip but only when pushed to the limit and when turned back will
gain grip very quick so it seems to have worked

i will check the price in the states

dan
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Old 03 January 2005, 13:05   #29
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Missing RPM

Quote:
Originally Posted by Bilge Rat
Searider is correct, stainless steel does not flex like ali therefore does not need to be as thick, rule of thumb is that if you increase pitch up your'll lose 200 rpm for every 2" pitch increase, so its interesting that Searider increased 1" and noticed no difference in rpm ?
It may have been that the boat is going a bit faster? Bow lifting a bit higher? allowing a few more rpm cancelling out the expected drop?

Have just got a 19" lazer II for the Scorpion to replace the 19" Vengence. Got about 1.5knots more speed and 100rpm more! How does that work?

Bought it secondhand from Pete7 for a reasonable price - if it had made no difference I could have sold it on for about the same price - FREE TESTING!

Selecting propellers, I think, is more trial and error than calculation.
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Old 24 April 2008, 15:49   #30
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I have a similar rig with 14 pitch 4.5 m Rib

I have a 450 rib-x with 60 merurcy 3.5 inch gear case.

The prop I have is a 14 pitch and it revs it nuts off!!!!!!!!!!!

They make a prop upto 19 pitch but they are quite hard to find.

There are two on ebaymotors in the US, but shipping is quited exensive.

I would happily but a new one if I knew it would be right but at |100 exh it could eb a costly mistake.

I ahve also seen a gadget on K4 Chandlery web sure that clips on the HT lead and records the RPM and the MAx RPM reached. Could be really useful................

Love to know what prop you settle on.........

Most second hand ones or ones in stock are 13 -15 pitch.

Chris
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