Overpitched Prop?

Cory B

Cory B

Sustaining Member
Hi all,

I know that prop pitch has been discussed on the site before, but I need a quick sanity check.

We have a 15" 3-blade maxprop (adjustable) on our 1984 Ericson 35. We also have the Universal 8424 engine (not the M25 which it seems everyone else has) rated at 24hp with a max RPM of 2800, and a 2:1 reduction gear.

Right now we have the prop pitched at 10.3", and are cruising at 2000RPM at about 6.3kts. Max throttle only brings it up to about 2200RPM and 6.6kts with a clean bottom in flat water. I've checked the RPMs with an optical tach, and I'm pretty confident of the speed numbers.

My feeling is that the boat should be able to go a bit faster than this under power, and that the RPMs are on the low side. The boat is going to be out of the water very briefly next week, and I'm thinking I should adjust the prop down one setting, which would put it at 9.2" pitch. Does that sound reasonable?

Also, what speeds are other 35-3 owners seeing under power?

Thank you,
Cory
 
K

Kim Schoedel

Member III
Cory, we have the sister ship to yours. But eith the 2 blade max and the m25. At 2000 rpms we do 6.1 to 6.3 knots. If I put the pedal down a bit to 2500 rpms we only gain to 6.5 to 6.7 knots. This is on flat water-no wind and fresh water lake. To us, it doesn't justify the extra fuel to only gain a few tenths of a knot. Oh, forgot to mention, towards the end of the season, she moves a bit slower especially early spring before we have the bottom scrubed. Happy sailing.
 
Steve

Steve

Member III
Sounds right

I also have the 5424 not the M25, clearly it's a low RPM high torque unit. I run about the same as Kim with the original two blade prop. I remember a few 7.0 kts with a tail wind, full throttle at +-2300-2400, I think 2800 is max with no load. Typically we run 5.5 - 6 at 1800 -2000. I don't want to make a big deal out of motoring, the wife is already eying trawlers.. yikes -I'm not old enough!

Steve
e35-3 #156
 
Cory B

Cory B

Sustaining Member
Hull Speed

Thanks for the input.

I'm surprised at the speeds under power you are getting, I was expecting a bit higher.

Hull speed for a 30 ft waterline (which is about what the 35-3 is what it gets moving) is approx 7.3kts, and it should be a fairly easily driven hull, provided the power is there.

I'll probably still repitch the prop, and I'll let you know my results. Nice thing about being adjustable is that we can always dial it back up if it doesn't work out.

As a total aside, I think the 5424 is a good engine, but man is it heavy. 425 lbs for 24hp versus 295lbs for 27hp in a modern 25xpb. Hopefully weight translates into longevity...

- Cory
 
K

Kim Schoedel

Member III
Yep, I would like to get more motoring speed however we seldom motor long distances. BTW I think the 35-3 has a water line of 28'10''. Now, in my feeble state of mind (lack of sailing this week) I cannot remember what the formula is for calculating hull speed. Can someone help me with this? Thanks
 
F

Frank Langer

1984 Ericson 30+, Nanaimo, BC
Although I don't have access to my sailing reference books, I think the formula was 1.34 times the square root of the waterline.
Frank.
 
Cory B

Cory B

Sustaining Member
waterline

Static waterline length on some boats, like most Ericsons, is misleading. With boats with overhangs, as the boat accellerates it "falls" into its trough and picks up a bit more length (I think this was partly done to get "free" waterline length under the racing rules of the day, but it can look nice too). So anyway, I figure 30' waterline for our boat when moving for round number purposes, and thats how I came up with about 7.3kts hullspeed using the formula Frank mentioned.

- Cory
 
K

Kim Schoedel

Member III
Thank you for the formula. Off the original subject question: Can any of you 35-3 owners acheive hull speed on a beat? I have bounced up there a few times but can't seem to maintain it. In fact, bounced to 7.4 a couple of times.
 
J

joerun26

Member II
35-III Prop Response .....

I recently sent this question to Martec....

I have a 1987 Ericson 35 with a 3GM30F Yanmar inboard diesel engine. The engine is rated at 17.7kw (continous rating) at 3400 rpm. The maximum output rating is 20.1kw at 3600 rpm.

I have a Martec Eliptec 2 blad folding prop - RH16DX14P-3. Under power at approx. 3200 rpm I'm only able to average 6 knts (with a clean prop and bottom). I also don't have much "bite" in reverse making manuvering around marinas a challenge. I don't know if I have the correct blade (or pitch) for my conditions, but I'd like to reach hull speed for this boat and improve my performance in reverse.

Their response ...

If you have a 2.6:1 gear ratio the propeller you have should be correct.
The speed you are talking about, does seem a bit off, not sure what hull speed should be, but I am guessing around 6.5-6.75.
A 3-blade folding or feathering propeller, would without question improve reverse, and probably make a notable difference in forward. Either would still provide good sailing performance and improve powering to something as good or better than any fixed propeller could give you. With a fixed prop you would look at losing 1/2 a knot to a full knot of sailing speed depending on whether it was 2 or 3 blade .

Anyone have a similar Yanmar and getting better performance ???


Joe
"Tenacious"
35-III # 262
 
Loren Beach

Loren Beach

O34 - Portland, OR
Senior Moderator
Blogs Author
I have always found the Martec staff to be friendly and helpful, and their answer seems logical and conservative. :nerd:

Speed : under light load conditions with a clean bottom I would kind of expect to see 7 kts or a shade over that at WOT, on your boat.
In this load condition our O-34 does 7.1. We have the original 1988 23 hp Universal diesel.

Reverse is where you need to capitalize every word in their write-up. ;) Folding props are disadvantaged in reverse, a lot. In forward, I would judge them to be very close to a fixed prop with the same number of blades.

A friend of mine with an E-33 went from a folder to a featherer ("Maxprop") a decade ago and instantly solved *all* of his reverse thrust problems. :rolleyes:
Our boat came with a fixed two blade and suffered from prop walk in reverse. I went with a Martec Autostream featherer when changing props.
As reported elsewhere here we gained light-air sailing speed (well Doh) and gained a lot a straight backing thrust.

I do not doubt that we could get another tenth or two in forward gear if we had an efficent fixed 3-blade prop, but this would slow down our sailing in light air even more than the former 2-blade fixed prop used to do.

"Everything's a compromise," as a friend of mine is always saying.

You did not ask, but if we were starting again... we would go with a 3-blade feathering, spendy item that they are. Virtually everyone I talk to sez that they balance better and make motoring a lot quieter.
As I remember, someone posting here regularly is trying out one of those more affordable New Zealand composite-blade featherers, and a search of the archives would seem to be in order.

Best,
Loren
ps: here is one of many other threads about this topic on this site:
http://www.ericsonyachts.org/infoexchange/showthread.php?t=3523&referrerid=28
 
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