Prop to Strut distance E38s

[juneausailin]

Hi all, I have seen a couple Ericson 38's, including one I just had surveyed, with a large distance between the strut and prop. The ABYC recomendation is that the distance be roughly the size of the diameter of the shaft.

Does anyone know why this distance is so much greater on Ericson 38's? Is that standard or do I just have a unique situation going on.. On the boat I had surveyed the distance was maybe 2-2.5 inches... 1984 E-38

Thanks,
David

 

[Sven]

On our 39B the distance is probably 6-7 inches. :eek:

That distance in undeniably too long. We got a very rough estimate of $4K to have a new strut made and installed when we last hauled, but it simply wasn't in the budget.

The reason for the distance is that it is needed to give the prop enough clearance. It would seem that the strut location was designed for a much smaller prop and that when an adequately large prop was installed it had to be further aft.

This is one aspect of Senta II that we are fundamentally uncomfortable with but we keep reminding ourselves that we have a sail boat, not a motor boat. We will just pay very close attention to vibration (when snagging kelp for example) and keep the revs lower than the Perkins would prefer (2.2k instead of 3k).


-Sven

 

[juneausailin]

Prop

I was thinking about cutting the prop shaft length down by about an inch to help out with that. I would up the pitch of the prop a bit and replace the fixed two blade with a folding three blade. Am also looking to re-power... currently has a universal 30 something... Any recs on the minimum engine size?

Opinions on whether this would do the trick for the 38?

Much thanks,
David

 

[Sven]

If you get the prop area and 10% (?) prop-hull clearance it sounds like a plan, if you really worry about the 2-2.5". Maybe you should instead use the clearance for a spur line cutter ... our distance is too large to make one useful

I hope someone else chimes in re. your question as I'm not even a prop-novice.




-Sven

 

[footrope]

Good question

I've heard that also. I can only offer that the shaft has to be strong enough, and supported close enough to the prop, that it doesn't allow the prop to bend the shaft out of alignment when stopped.

There is also a recommendation (rule of thumb?) about how close the tips of the blade should come to the hull to avoid cavitation. I was told that at least 15% of the prop diameter is desired and 10% is the minimum. Some props, cruise rpms,and hull shapes probably need the high end and others might tolerate less.

In 2009 I removed a prop saver from the drive train and brought the prop an inch closer to the strut. New tip to hull clearance is about 12% of the prop diameter. We've had no problems. We had the boat hauled for a survey and bottom paint in December 2010 and everything looked fine also (validating my alignment job). Obviously, if the shaft is true and the strut and cutless are good and aligned with the engine, and observing the appropriate prop-hull clearance recommendation, then you're probably OK. Maybe that's why the 38s have 1" shafts?

The pic is from 2005, with the prop saver installed to the transmission flange. Man, I should take a pic after everything is cleaned up someday.

 

[juneausailin]

Thank you all

Thanks for the feedback all. Footrope, what is the diameter and Pitch on your prop? Looks almost identical to the set up on the E38 I am in the process of purchasing..

Much thanks,
David

 

[footrope]

Hi David,

You're welcome. I have to go to the boat to get the prop dimensions. It's a bronze, three-blade, feathering Max-Prop. It uses the 63-size zinc. It's holding up very well and does a great job moving the boat in both directions. It was on the boat when we bought it in 2003 and all I've done to it is clean and grease it on haulouts and keep fresh zincs on it.

Craig

 

[rwthomas1]

There is 1 1/2 inches clearance prop-to-strut on my E38. That said I installed a Variprofile 3 blade feathering prop that mounts to a stub hub installed on the shaft. This places the prop at least 3" back from the old fixed location. No vibration, no issues. The Variprofile is the second best thing I have added to the boat, the first being a belowdecks AP. RT

 

[juneausailin]

Fyi

I talked to slip stream and they did the math... Ended up getting a Slipstream three blade geared 15RH11.5 and was able to cut about an inch and 1/2 off the prop shaft and reduce the distance between strut and prop to the recomended 1" for a 1" shaft.