E27 RPMs vs. Knots

[rgoff]

I finally installed a tach on my 1973 E27 (with original Atomic 4) I've had for 20 years! Tried it out the first time yesterday.

Idle reads around 600 RPM, which sounds about right. Behind the breakwater in calm water I was doing a bit over 5 knots at 1250 RPM. This seemed like low RPM for that speed to me.

Is this reasonable? What is normal cruising RPM at sea (not in the harbor) for you other E27 owners?

I think the original owner said he'd replaced the stock prop, but I don't know the specs on the current one.


Thanks,

 

[Walter Pearson]

Measured with a hand operated tach on the engine shaft, I got 1465 rpm at 5.4 knots and 1730 rpm at 5.9 knots. Knots measured by GPS. This was with a CDI prop on Atomic4 1976 E27. Since then have changed to Indigo prop, but haven't repeated rpm vs. knot test yet. My ear tells me rpms have increased.

 

[Joe Benedict]

Which Prop

I'm also looking at the prop issue and other things as my boat is in it's cradle for the winter (please no salesmen need respond.) My '77 e29 has similiar prop needs. The RPM's do seem a bit low as everything I have read/been told indicates the correct RPM is 1600. Are you sure there isn't some kind of a governor or throttle stop installed? The prop size should be stamped on the body of the prop or on the end where the nut is (it may be covered by a washer.) The original was a 2 blade and should say something like 12 R 7 which is 12" diameter, right rotation, and 7" pitch. Walter, how do you like the Indigo? What I need is more docking manuverability not speed. I really don't want to shell out the funds for a Max-prop - sail work is number one this season. Again, no salemen need respond.

 

[Seth]

props and salesmen

Joe,

If that comment was directed at me, please accept my apologies if I have put you off. My presence here on the site is primarily to assist Ericson owners with the experience I gained while working as the customer service/warranty administrator at the Ericson factory.

During these last 2 years I worked for Doyle Sails, and yes, I have sold some sails to this group, but I have worked very hard to keep all discussions about selling sails out of the public forum and only via private communications-just for this reason-I am NOT motivated here by the promise of selling anything.

In fact, I regularly give advice and support to those owners who prefer to work with their own sailmakers-even if the questions are about sails.

This forum is not meant, not do I use it, as a commercial outlet.

I have retired from sailmaking anyway. I can and will coordinate new sails for those who want me to-but this is very much a secondary consideration.

Again, my apologies (to all of you!) if you got any other impression of my motivations.

Seth Morrell
now a non-industry contributor

 

[Joe Benedict]

Back to the question

Seth:

My comments were not directed towards you. As near as I can figure, you have provided a lot of useful information to many people. My comment has to deal with other instances unrelated to this site. I have a Doyle mainsail and the Chicago loft has done work on other sails on the boat for the previous owner. If I can get my schedule organized, I will try to stop by at Strictly Sail Chicago - or if I can't I will contact the loft directly. In any case please accept my apology.

Getting back to the RPM/prop question. This issue is the subject of several strings and I believe people would be interested in real conversion updates.

 

[Seth]

Salesmen

No worries-Since there is virtually no commercial activity here it seemed like that was what you were implying-I am the closest thing to that on the site, but again-not my real motivation (even less so now that I am 'retired").

Moving forward, let me know if I can help.
Cheers

 

[Walter Pearson]

Joe,
The CDI prop was a noticeable improvement over the original 2-blade bronze 10X6 prop. I was looking for more control for backing and it did make a difference, however it also dropped the RPMs too. I had a marginal cooling issue and thought more revs would help and also give me more power if I really needed it, so went to the Indigo. I have not had a lot of experience with this one yet, but initial reaction is the backing performance is equal to the CDI and the RPMs do appear higher under similar conditions, but have not measured yet.

 

[Joe Benedict]

Walter:

That's what I needed to hear. Most information talks about speed not manuverability. Quarters are a little tight at North Point Mariner and unless you get caught in a storm you only need to motor about a mile. It's probably too early but did you notice any plug fouling with the low RPM? This later question also could be of assistance to rgoff.

 

[Walter Pearson]

Joe,
I've never noticed any plug fouling problems. I have a short season and use the engine sparingly, so may not be the best to address this issue. A couple seasons ago I also started using the hotter plug, so comparisons are difficult.

 

[Joe Benedict]

CDI Exit Prop Business

Walter,
I don't run the engine much either and I'll launch about May 14 and haul out about Columbus Day. Any carbon residue is probably due to idling and not engine load. I noticed the CDI furler page no longer contained a reference to props so I contacted them. They no longer offer the prop. The good news is that it's one less option to consider - the bad news is it's one less option to consider.