What size prop do you have?

Bower15 said:
I'm surprised your prop is so big, how many HP has your engine? Using the propcalc link in your reply suggests that i need a 10x8" to reach a max speed of 5 Knots and 10x6 to reach 4 Knots which is similar to the figures i had before. I used a prop calculator from a company in Canada which required a lot more info but came up with similar results.
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The Yanmar is 9hp (even though it's called a gm10), and I allowed 1hp drop through the gearbox. No black smoke at full revs, so it can't be far out.
 
12 x 7 prop nay use?

Hi, I have a 12 x 7 prop on a 1" taper but it is left hand, that is, it needs to turn the same direction of an engine runnig clockwise from the front end.

PS I live in Scotland.
 
" Quidi Vidi, Invader 22ft, Bilge keel, built 1980 sail No 538, 6HP Petter diesel"


Dry out, tape measure, look for details on prop, phone sillette or someone similar...... hand in pocket, ....dry out again..... sorted :):)
 
Getting the prop off.

If you are planning to try and remove the prop between tides, you may be as well to get a three legged puller as the prop may be well and truly stuck on.

J.
 
But you would not be able to do that with a Petter that produces less than 5 real hp on a good day and a 2:1 box!
 
Thanks Steve, proves my prop would be better suited to a boat and engine your size
J, good idea, I have started asking around for one
The plan at the moment is to book onto a grid, remove the prop, scrub off and anti foul and then return to my mooring using a 4HP outboard. Then take my time cutting down the existing prop over a week or so and then back onto the grid to refit it. At least I don't have to worry about tapers etc just need to make sure it's balanced properly. As with all well laid plans it will probably not go according to plan but it will be fun
 
Jcorstorphine said:
If you are planning to try and remove the prop between tides, you may be as well to get a three legged puller as the prop may be well and truly stuck on.

J.
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I made one from scrap 18mm ply: Two pieces with slots cut in to fit over the shaft (tight-ish fit) and one with no slot, plus 3 pieces of 12mm threaded rod ('cos that's what I had - 10 would probably be fine), plus nuts and penny washers. The holes in the slotted bits are drilled so the slots are opposite each other and the rods will miss the blades. Holes in the other piece so the rods will fit.

Slacken the prop nut a few turns, making sure there's still plenty of it threaded on the shaft - you only need to move the prop a couple of mm to free it. Put the slotted bits behind the prop and the unslotted one over the nut and tighten the nuts on the threaded rods evenly.

A piece of slotted metal between the slotted pieces and the prop and a disc against the prop nut will help spread the load and give you a better chance if it's stuck. If all else fails, tighten the rods as tight as you dare and take a blowlamp to the prop.
 
Just to spur you on a bit, I had a very similar problem on my boat where the previous owner had re-engined from an 8hp yanmar to a 10 hp volvo and just left the old prop on. The problem was that the gearbox ratios were very different and the old prop was way oversized. I just used one of the online calculators and fitted what it suggested - it made an absolute world of a difference and my engine is a lot happier now, it revs a bit higher, but much more smoothly, and the difference when fighting the wind or a chop is significant. I think it was 13" diameter, which is the max I can have, so it was just the pitch that was changed.
 
Thanks Stemar, just the kind of project that I like. I'll use your idea if I can't scrounge a puller from somewhere.
Had a reply from Sillette today recommending I use a 10x7" prop based on the info I provided them with. So it seems my calculations were about right and that I am seriously overpropped.
 
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