Islander 28 propeller location from shaft support? - SailNet Community

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Old 04-14-2013
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Islander 28 propeller location from shaft support?

I'm going to replace my prop shaft, its bent, worn in grooves, and appears to short. My prop is within an inch or two of the shaft support. I bought the boat with an electric motor, and the prop shaft has most likely been moved forward to connect to the electric motor or the shaft may have been shortened.

So, I know prop to hull clearance is important to performance and noise level. I have a 3 blade, 12x 10. The electric motor likes props similar to diesels.

I was going to get a new shaft and prop set up.
So, I was wondering where most if the 28 guys had their props sitting from the support and rudder?

What size and type prop the diesel guys have?

Your input would be greatly appreciated
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Old 04-19-2013
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Re: Islander 28 propeller location from shaft support?

WOW, no help.

This is why I have posted detailed information and pictures of important fixes for the Islander 28, seems help is most likely non-existent or long time coming.

I guess another area I will need research and post my findings.

While there are plenty of places to get information about propeller to hull clearances and distance from rudder, every boat is different with how they respond to certain changes.

There are fewer Islander 28's around then Catalina 27, so just takes longer to get the help, I'm OK with that.

I like a small cozy community, or a Catalina owner saying," nice boat, who made it, looks like the lines of a boat during the late 80's, what year is it?, what? a 1976? Where can I get one?

So, still waiting for help.
Thanks
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Old 04-19-2013
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Re: Islander 28 propeller location from shaft support?

Quote:
Originally Posted by 510datsun View Post
I'm going to replace my prop shaft, its bent, worn in grooves, and appears to short. My prop is within an inch or two of the shaft support.
Sounds perfect!

rule of thumb 1 to 2 times the diameter of the propshaft from the last support

so with a 1 inch shaft what you should have 1-2 inch would be ok
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Old 04-19-2013
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Re: Islander 28 propeller location from shaft support?

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Originally Posted by divefreak View Post
Sounds perfect!

rule of thumb 1 to 2 times the diameter of the propshaft from the last support

so with a 1 inch shaft what you should have 1-2 inch would be ok
Thank You very much for the help!

I will check it to make sure.
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Re: Islander 28 propeller location from shaft support?

Anyone out there that can answer about what prop is being run on the diesel power units?
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Old 04-19-2013
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Re: Islander 28 propeller location from shaft support?

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Originally Posted by 510datsun View Post
Anyone out there that can answer about what prop is being run on the diesel power units?
Prop size and pitch involves calculations using the engine HP/torque, the transmission ratio, hull, and number of blades. You could expand the pool of people who might be able to answer if you could give values for all the variables.
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Old 04-19-2013
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Re: Islander 28 propeller location from shaft support?

Don't remember a damned thing except it was a Martec 2-blade folding prop, and unless memory fails me, we had room for two good sized zincs on the shaft in between the prop and the prop strut, making it maybe 5? 6? inches from the strut to the back of the prop.

If nobody turns up with an answer, try looking at some of the PHRF fleets in the midwest or northeast, you may be able to contact another I28 owner directly that way.
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Old 04-21-2013
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Re: Islander 28 propeller location from shaft support?

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Originally Posted by dacap06 View Post
Prop size and pitch involves calculations using the engine HP/torque, the transmission ratio, hull, and number of blades. You could expand the pool of people who might be able to answer if you could give values for all the variables.
I'm guessing you didn't read the first message I posted at the start of the thread, but I will recap it for you.

In my initial post at the start of the thread, I stated I have an electric motor. The HP rating for electric and combustion engines is different because of the character differences of the two. I have been told the electric motors are more like the diesel vs a gas, more torque, and lower RPM versus a gas motor. So, trying to us a general formula for a combustion engine I don't think would work. An electric 5 hp rated motor would be close to the out put of 10-15 HP gas, so I have been told.

I don't have a transmission, but my pulleys are 2:1 from the motor to the prop shaft. Would be hard to plug my set up in to the formula.

I also initially posted, I have an Islander 28, I'm guessing since you wanted a hull, I have a 1976, hull #23. I was just trying to get an idea of what the diesel owners of the 28 were running to compare their's to what I have, to see if I'm OK with what I have.

In my first post, I stated I have a 3 blade 12x10.

So, kinda back to my initial question at the first post.

What prop are the owners of Islander 28 with diesel engines using?

Just looking for a general feel from the Islander 28 community

Thanks for wanting to help out, says a lot.
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Old 04-21-2013
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Re: Islander 28 propeller location from shaft support?

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Originally Posted by hellosailor View Post
Don't remember a damned thing except it was a Martec 2-blade folding prop, and unless memory fails me, we had room for two good sized zincs on the shaft in between the prop and the prop strut, making it maybe 5? 6? inches from the strut to the back of the prop.

If nobody turns up with an answer, try looking at some of the PHRF fleets in the midwest or northeast, you may be able to contact another I28 owner directly that way.
Thanks, I will give that a try.
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Old 04-21-2013
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Re: Islander 28 propeller location from shaft support?

"I bought the boat with an electric motor,"
Could easily be read to mean you bought it with an electric--but are in the process of restoring the proper diesel engine. Since the usual prop would be relevant for the usual diesel engine, not the electric.

Either way, David Gerr has a "Propellor Handbook" out there. From the displacement of the boat, the engine speed, etc. there are formulas for figuring the correct prop to use. That would be another way to go, and to verify differences from the diesel setup. Although I'd figure, the same prop at the same prop speed should be used for the same boat, regardless of what was driving the prop.

A good prop maker might even know what they've sold for the boats before.
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