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Guys,

 

I have a chip in my prop blade, and I'm thinking of getting a higher pitch on it's replacement.

 

For those of you running a GBE or similar, what pitch are you running on your 9.9hp?

 

My rig is 2800 to 3800 pounds GBE variant with a 9.9 Yamaha four stroke "high thrust" and a 11 3/4" by  9" pitch prop.   Top speed is about 7 knots with a clean bottom.

 

Thanks!

 

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Hi paxfish,

 

A lot of the boats here run 2 stroke 8 HP as that is the lightest motor they can carry for racing, and would be propped slightly differently.

 

Personally On my GBE I have a newer version of your motor with the high thurst as well. My logic is that I am happy to sacrifice a knot or two of top speed in return for very positive response while manoeuvring and the knowledge that if the weather is bad there is heaps of low speed grunt on tap to get out of a sticky situation

 

Cheers

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Keep the old chipped one on board, if its the rubber bushed version they can spin the bush out and will (maybe, if your really lucky) still motor at bugger all revs only. Usually happens when you dont want it to happen, short chop, lee shore, semi darkness, raining, family on board, cruising, etc. So nice to have the old one with a fair dinkum bush on board. 

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Keep the old chipped one on board, if its the rubber bushed version they can spin the bush out and will (maybe, if your really lucky) still motor at bugger all revs only. Usually happens when you dont want it to happen, short chop, lee shore, semi darkness, raining, family on board, cruising, etc. So nice to have the old one with a fair dinkum bush on board. 

 

Thanks for the responses, Gents!   Very Helpful.   Especially yours, BNG!

 

P. S.   Has anyone seen my down under translator lying about?

 

:razz:

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Really elementary prop selection guide.

 

When you boat is clean, but has it's average load on board, your engine should just reach it's max allowable revs (check the manualunder full power in calm conditions. If it does not, it is over-proped, if it reaches max revs with more than a little throttle still available, it is under proped. A little under-proped is good, as it allows for more load and or weather conditions. Be sure you cannot over-rev you motor, esp an outboard or other petrol engine (Diesels are governed and cannot be over rev'd when working properly).

 

Most little outboards don't have a rev counter, but you can get one pretty cheaply, including handheld optical ones for testing, not permanent install.  Or borrow one. 

 

Correct prop sizing is good for your engine, gives best economy, and best boat speed under power. It is worth the effort!

 

Finally, if you have a prop with a bush that has died, and you need a temp solution, a couple of screws thru the hub into the bush often works for a while, provided the failure is the outside vulcanising..... NOT a permanent solution!! As BNG said, carry a spare prop.

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Keep the old chipped one on board, if its the rubber bushed version they can spin the bush out and will (maybe, if your really lucky) still motor at bugger all revs only. Usually happens when you dont want it to happen, short chop, lee shore, semi darkness, raining, family on board, cruising, etc. So nice to have the old one with a fair dinkum bush on board. 

 

Happened to us last year of a windy day when we had broken half the slugs off the main. Ended up limping to a local yacht club where we had a few rums and waited for the wind to drop before motorsailing home under jib.

 

The props (on 8hp Yamy long shafts anyways) can jump in an out of the water a lot when trying to motor in a chop and I think that busts the bush.

 

Prop selection for our cats is tricky due to the windage we have. We have changed to a prop with reduced pitch which means we can only motor at about 5-6knots in flat water but we get a lot more grip/push when the wind comes in, where the old prop would just labour the motor with the extra load. We have also added one of those trim wing things which has reduced the ventilation problem in a chop.

 

I was very impressed with Ed's 9.9hp motor when I went for a sail with him. It was so quiet that I forgot to turn it off before raising it! The bigger diameter prop gives a good grip on the water. Actually I was very impressed with it until we start sailing and the motor bracket started spraying water at me like a firehose!

 

I hope the electronic switchboard you have in the engine well is well waterproofed as that areas sees a lot of water when sailing.

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Thanks for the comments, Freedom -

 

Yeah - that is a Blue Seas switchbox and it is rated for exposure.   I opened it up, hosed down all the contacts with Corrosion X and resealed it.   Hopefully it continues to hold up well.

 

That box is for the nav lights.   I have a separate system with it's own battery, solar panel and controller to power the GPS and autopilot.

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For pushing multihulls ( or dare I say any displacement yacht or even small barge) you want big blade area, big diameter and fine pitch. Think of a prop moving through butter like a screw. If you are going fast, say 20-30 knots, which is what most outboards are aimed to do, then you need a course pitch to keep the prop gripping at its high speed through the water. But that same high pitch prop will stall the blades at low speed, especially in reverse. A bit like having your sails over sheeted going downwind.

 

The ideal is 'under square' which is less pitch than diameter, but can be hard to find. Much as I really hate to use anything imperial, you should be looking for a 10" x 8", or 9" x 6" etc. Biggest diameter the motor will take, smallest pitch you can find.

 

The ongoing popularity of a the Yamaha 9.9 as a yacht motor is they are one of the few with a low gear box, a big prop for the motors size, and 'barge pushing' prop options. The real difference is reverse and low speeds. But your yacht can't motor at really high speeds anyway; the hull shape won't let it. 

 

PS: Not sure in NZ what a pound is with relation to a boat? Are you a drummer or pile driver?? 

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After struggling with pushing Deeds along in strong winds I changed to the smaller of the 2 High Thrust props available for the 8hp Yam. I can now motor in 30 knots which is really nice.

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