Propeller to hull clearance

Is there a rule-of-thumb or a standard that refers to a minimum or optimum propeller tip to hull distance for a given horsepower & prop combination? I have a 17.5 inch diameter, 3-blade, feathering propeller. The engine is the 5432 Universal, 32 hp. The new dripless shaft seal is quite different from the old one and the result is that I can't fit the red plastic prop saver between the transmission and the shaft couplings. That moves the prop forward about an inch and reduces the prop tip clearance to about 2-3/8 inches.

Just eye-balling it, there's maybe a 1/4 to 1/2 inch less clearance now than before. I don't imagine it makes much difference, but I thought I'd see if the board had some knowledge.

Thanks.

PS - the new PSS bellows collar that fits over the stern tube is thicker than the old one (in fact it's two pieces glued together with contact cement), making it necessary to grind some excess resin "flash" from around the underside of the stern tube so that the clamps would fit. This may be a characteristic of my boat, and not others. The other difference is that the carbon fitting is longer by about 3/4 inch to make room for the mandatory 3/8" vent barb to thread into it. The vent is forced on us low speed guys now, unless we void the warranty and plug it. It was a real tight fit before and now it's impossible to fit the donut in there.

If I recall, the min. is 10% of the dia. and better if you can maintain 15%. HP is not the criteria, just clearance.
Anyone else??
Class?

Loren

The 10% rule is what I got from Maxprop when I switched to their propellor.
They're very knowledgable and helpful - give 'em a call with specifics.

Prop Clearance

I recently repowered, went from roughly 18 hp to 30 +hp ( a 2GM20F out and 3HM35F in)
When selecting the gear ratio I was very limited for prop diameter as part of the equation. The existing setup was utilizing a 13" dia. fixed 3 blade with roughly 1" of clearnace.
Did some rough measurements and determined that I had some excess thickness at the centerline hull joint on the I31. Decided to go with a 14" dia./ extend the shaft somewhat for more overhang and remove some of that surplus fiberglass for clearance.
Went with a 2 to 1 reduction gear in place of the 2.6 to 1 on the 2GM and seem to have come out about right.
With a relatively small wheel/ prop I've got roughly 1" clearance, obviously far less then the 10% factor. Ran it for a season now and there's been no tendency to cavitate.
Based on this experience I would suggest you should have no problem with your 2-3/8" clearance.
I'm in the same distress with the dripless, I was looking at the stern tube today as a matter of fact to see where I can gain some additional length as well for a PSS assembly. I also want to retain the newly added vibration dampner in the driveline and it appears I may have a hope. It looked today as if I could as well remove some filler below the stern tube to gain the needed length. To accomodate the 1" PSS assembly I need 6-1/4" for the 1" size so I need to gain about an extra inch.
When laying out the repower we placed the newer Yanmar such that there's basically "0" clearance to the companionway panel. Actually had to carve a 1/2 moon relief in the backside of the panel to clear the upper pulley.

Hi Craig, hope you make out ok, how about some pics as this is something I would like to accomplish also. Where are you hauled at? I would like to throw an eye on it if possible. Would some Kilt Lifter help?
Harold

hodo said:

Hi Craig, hope you make out ok, how about some pics as this is something I would like to accomplish also. Where are you hauled at? I would like to throw an eye on it if possible. Would some Kilt Lifter help?
Harold

Click to expand...

Harold,

I have some before photos, but need to take some after shots once I get the other 3 bolts installed. I will post some here. I recall you have the same engine arrangement as mine - under the steps - so I could give you a few pointers and cautions. I would be happy to have you come up and take a look. We're at Delta Marine on the Duwamish River, back in their small boatyard. If you can climb a 12' ladder and drop down into the starboard lazarette, you'll get a very good view of the installation. A cold Kilt Lifter is always appreciated.

I wish I'd taken pictures of the bellows before nailing it in there. I think they made a production improvement (saves $) that permits them to use the same bellows part for several stern tube diameters, just by picking the correct rubber adapter to stick in the end. I test-fit the bellows so many times that the glue gave way. It was annoying to have to grind away the resin. I was kind of worried about gouging the hull.

The steel donut with the two O-rings that fits around the shaft annoys me too. (I need to vent to PYI about this.) The instructions say not to use any oil to help ease the donut onto the shaft. But, with zero extra room, and using anti-seize on the coupling and the coupling bolts & nuts, you got to be really careful not to get any on the shaft beyond the back end of the coupling. I hope I didn't get any excess back there. I used as much care as a one-armed man can. I can't see any, but I'm not done fumbling around with bolts, nor have I positioned the steel donut to compress the bellows.

The point is, why do these particular O-rings have to be made of material that is sensitive to petroleum products? Same curiosity about transmission seals and penetrating oils. I'm sure there's a good reason, durability or heat resistance, but it sure is annoying.

Contact me back-channel and let's get together. I am trying to get her back in the water in January. I don't go back to work until Jan 5th.

Cheers,

If I remember correctly, Teflon impregnated "O" rings need to be installed dry. Viton "O" rings can use either KY water based lubricant or petroleum based lubricant.

Thanks for the info, guys. Now it's time to check shaft alignment.

Free Install Manual !

Check out www.westerbeke.com -Technical -Install Manual - Page 11
The recommended prop to hull distance is .15~.20 x prop diameter.
Do not attempt RePower or leave home without this Manual :nerd: