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Old 22-03-2015, 11:24   #1
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Change propeller.. things goes worst..

I replace the propeller on my islander 30.
From a 13/13 two blades, we passed to a 13/13 3 blades..
I tried this morning but I noticed:
1) I cannot go up from 15k rpm, or everything shake inside the boat
2) Engine temperature goes really high
3) No power, we just move at 1 knot.. for a short time I saw 2.4 knot when I move down the rpm
Any suggestion?? shaft alignment?? transmission?? any suggestion would be appreciated it.
Engine is a volvo md7 (13 hp I think)
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Old 22-03-2015, 11:43   #2
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Re: Change propeller.. things goes worst..

You are now massively over proped. The 13/13 3 blade sounds like it won't work with your engine. Which is no surprise if the 13/13-2 was reasonable.
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Old 22-03-2015, 11:54   #3
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Re: Change propeller.. things goes worst..

Sounds like you're over-propped. 13 x 13 x 3 is pretty big for 13 hp.
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Old 22-03-2015, 12:04   #4
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Re: Change propeller.. things goes worst..

Ufff!! The propeller was suggested by Olimpyc Propeller on Annacortes.. I was asking about something with less pitch in order to compensate the extra blade..
With the 2 blade I got 3/4 knots at full rpm (2600) so I tough with a 3 blades could get some extra power..
Any suggestion other than send back the propeller for replacement??
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Old 22-03-2015, 12:44   #5
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Re: Change propeller.. things goes worst..

You said the new prop is the same diameter and pitch as the new prop but is 3 blade instead of 2. The new prop is apparently overloading your engine. A prop shop should be able to recommend a prop that will produce optimum speed for your engine, hull and displacement. Whether that will be more than 4 knots I don't know. Keep your bottom clean for top speed.
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Old 22-03-2015, 12:52   #6
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Re: Change propeller.. things goes worst..

I would guess that a 13 x 13 3 blade prop is about right for your boat IF you have a 2:1 gear ratio.

You'll know it is over propped, if the engine exhaust has a lot of black smoke.

For more than a guess of correct prop size, the gearbox ratio; displacement weight, and water line length of the boat are required.

Since you didn't mention black smoky exhaust, I'm thinking the problem may be the propeller taper is not correctly matched for the shaft, and it is mounted crooked causing an imbalance.
Pull it out of the water and ensure the prop is tight with no movement from side to side. Spin it and measure the distance from each blade to a fixed point such as the rudder. They should all be exactly the same. I expect you'll see a wobble.
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Old 22-03-2015, 13:06   #7
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Re: Change propeller.. things goes worst..

If you want to calculate optimum prop size for your boat, here is a great little excel spreadsheet to work it out. It has calculations for 2, 3 & 4 blade props.

Propeller Calculator / Prop Calculator

scroll down a bit until you see- Surfbaud Freeware Propeller Calculator
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Old 22-03-2015, 17:49   #8
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Re: Change propeller.. things goes worst..

Vic prop also has an online calculator.
Vicprop - Prop calculator for Displacement and semi-displacement hulls
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Old 22-03-2015, 18:54   #9
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Re: Change propeller.. things goes worst..

Quote:
Originally Posted by Kokanee View Post
I would guess that a 13 x 13 3 blade prop is about right for your boat IF you have a 2:1 gear ratio.

You'll know it is over propped, if the engine exhaust has a lot of black smoke.

For more than a guess of correct prop size, the gearbox ratio; displacement weight, and water line length of the boat are required.

Since you didn't mention black smoky exhaust, I'm thinking the problem may be the propeller taper is not correctly matched for the shaft, and it is mounted crooked causing an imbalance.
Pull it out of the water and ensure the prop is tight with no movement from side to side. Spin it and measure the distance from each blade to a fixed point such as the rudder. They should all be exactly the same. I expect you'll see a wobble.

Thanks!
I got smoke.. a lot.. not black but white and engine really got hot..
My transmission relation is 1:1.9 very common on small volvos
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Old 22-03-2015, 19:03   #10
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Re: Change propeller.. things goes worst..

...Vic prop show me max pitch should be 9.3 and I have 13...
We're gonna move out water the boat tomorrow.. to check shaft alignment and transmission just in case..
But seems like I got the wrong pitch for this engine/transmission combination...
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Old 23-03-2015, 00:54   #11
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Re: Change propeller.. things goes worst..

The original and the new prop appear to be oversized. The new one even worse.


13hp is a bit low for a 30ft boat but in calm conditions, it should still be able to get you up to 5-6kts.
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Old 23-03-2015, 16:25   #12
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Re: Change propeller.. things goes worst..

You're just vastly over-propped now. Any reason in particular that you needed to change? What was wrong with the original 2-blade?
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Old 27-03-2015, 07:09   #13
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Re: Change propeller.. things goes worst..

My understanding is that if the pitch and diameter are kept the same, that going to a three blade prop decreases the surface loading (good if you have a cavitation problem) but does not substantially change the engine load. If I recall, your pitch need only go down 5% or so when increasing to 3 blades. Dave Gerr's "Propeller Handbook" is an excellent reference. Are you sure the original and current prop is accurately identified?

Your symptoms sound like either a out of balance prop/shaft, bad cutlass bearing or dirty prop. How long ago was it installed? And it has to be spotlessly clean to make any determination as to overload.
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Old 27-03-2015, 21:08   #14
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Re: Change propeller.. things goes worst..

.Upgrade.. All this week I work closely with yard in order to find the culprit.. I replaced engine support, alignment was checked 4 times!!, strout.. everything you can think was checked... definitely prop was over sized...
Contact Olympic Propeller on Annacortes.. they're not take the wrong one because is "used" (WTF???).. Offer me first repitch to 13/9 and, ultimately, get a new one..
WTF?? they sold me a wrong one, not want to change and now offer me another one at a "special" price???
..these guys are simply too much for me.. Now I have an expensive paper weight, no solution for my prop, my boat is on the yard, cost are higher due the amount of hours yard put and travelift used.. and I'm not have a boat while think get a new one (and invest more money), tried to repitch for another $300 or use C4 and blow the whole boat... Definitely I never gonna do business again with Olympic Propeller and I gonna do everything on my hand in order to clear this matter by a legal way... I'm very mad...
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