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E35-3 correct prop/pitch

G

gabosifat

Member III
Hi All,

I have an 86 E35-3 with a newer Universal 30hp/4cyl engine & a MaxProp. I'm trying to decide if I have the correct pitch on my prop. Does anyone know the correct hull speed for these boats? Right now I'm running at 6.2 knots at 2700 rpm. This rpm is just above the recommended cruising rpm. They recommend 2200 to 2600. I'd like to increase the pitch & drop rpm to 2200-2300. The engine noise and vibration are excessive at 2700 and smooth & quiet at 2300. I am of course concerned with overloading the engine & shortening it's lifespan.

Would appreciate any comments of those who have addressed this issue.

Many thanks,
Steve Gabbott
Vancouver BC
 
T

Tom Plummer

Member III
The specs page included in the E35-3 Review from Pacific Skipper Magazine found on the Specs & Documents page of this site says that your thoretical hull speed is 7.2 kts. So it would seen that your prop is under pitched.
 
T

ted_reshetiloff

Contributing Partner
There are several theories on this subject but I have always been told to set your pitch so that the engine will achieve its maximum rpm (see engine specs) at full throttle. You engine's HP/torque curves tell you at precisely what rpm your engine will produce its maximum power. That will allow you get the most out of your engine based on its design. Over or under pitching will likely cause greater than designed for strain (lugging, over revving) on the engine and shorten its lifespan. A word of caution on rpm for diesels, make sure to have your tach calibrated before making other adjustments. To have that done you either need to buy a special tool or have a mechanic who has one come and check it for you.
 
G

Geoff Johnson

Fellow Ericson Owner
Or you can install the TinyTach (about $65 as I recall) which works by measuring the pulses in the high pressure fuel line through a bolt-on transducer.
 
u079721

u079721

Contributing Partner
Underpitched

I went through the opposite of this problem with the Max prop on my 38.

As noted above, you need the correct pitch on your prop to attain the suggested max rpm of your engine at full throttle. You should also check your tach for calibration before working on this. See if you can borrow or rent a strobe tac from a friend or auto shop first.

Then you need to open up your Max prop the next time you haul and check the settings to determine the present pitch. On my boat the 16" diameter 3 blade prop was originally pitched by the PO to 13.4". This gave me a top rpm of just 2100, no where near the spec of 2800. I tried dropping this to 11.0" of pitch, but the rpm only went to 2550. So the following year when I hauled I dropped the pitch further to 9.8", at which point the max rpm was then 2850, or pretty close to the suggested max.

Not knowing your present max rpm or present pitch we can't really provide a guess as to how much you have to change. But the goal is to get the engine to be able to just reach its max rpm. After that, follow the suggestions in the manual for the cruising rpm (I used 2300 to 2400 for up to 24 hours at a time with our M40). Whatever speed you get then is the best you are going to be able to do with that engine and prop.
 
T

Tom Plummer

Member III
ted_reshetiloff said:
There are several theories on this subject but I have always been told to set your pitch so that the engine will achieve its maximum rpm (see engine specs) at full throttle. You engine's HP/torque curves tell you at precisely what rpm your engine will produce its maximum power. That will allow you get the most out of your engine based on its design. Over or under pitching will likely cause greater than designed for strain (lugging, over revving) on the engine and shorten its lifespan. A word of caution on rpm for diesels, make sure to have your tach calibrated before making other adjustments. To have that done you either need to buy a special tool or have a mechanic who has one come and check it for you.
Click to expand...


The difficulty with the full throttle method on deisels is that they are goverened. When you set the throttle you are actually setting the govener.

This means that in order to use the full thottle method you have incramentally increase the pitch until the engine just fails to reach its factory rated max rpm and the back off until it will just will reach max rpms.

Another method is to set the pitch so that the boat operates at hull speed at factorys recomend normal operating RPM. I favor this method because you are less likely to grossly over pitch the prop. This is particulary important if you have the old style Maxprop which must be dissasembled to change the pitch this make a haul out pretty much a requirement every time you change the pitch.

Both methods are done flat water.
 
G

Geoff Johnson

Fellow Ericson Owner
I'm no engine whiz, but I don't think a strobe tachometer is going to work on a diesel since it requires an ignition system. I have found the TinyTach to work very well as does an old dial tach I bought on eBay. As for the MaxProp, which I have, there is a formula on the PYI site somewhere that tells you how much to change the setting for a given increase in rpm's. So once you know what rpm's you are turning and what rpm's you want to get to, you can change the setting accordingly. My engine was lugging a bit, as evidenced by the black soot on the transom, so I had the prop repitched so that I can cruise @ 6 knots at 2400 rpm's. Engine (M25) seems happier.

Finally, changing to a Balmar alternator threw off the OEM tach (which was off by 200 RPM's anyway), but the difference is a linear relationship so I can still use it (e.g. 3000 rpm's is really 2300.)
 
Last edited:
Loren Beach

Loren Beach

O34 - Portland, OR
Senior Moderator
Blogs Author
On our Universal diesel, there is a maximum number of revs, and then there is the factory-specified cruising revs, and the later is about 2400 to 2600. I have run 'er up to 2900 a few times... just to see what happens... and the boat will then go about 7 kts on a smooth bottom -- engine sounds a bit too busy at those revs, IMHO.
:rolleyes:

Loren in PDX
1988 Olson 34
 
G

gabosifat

Member III
E-35 prop pitch

Many thanks to all who responded to my question on the prop pitch. I have checked the Maxprop formula & a 2 degree pitch change (changes rpm by 13-15%) would drop it down to where I want to be. I know it's too low now as the engine easily reaches the max RPM of 3000 and is quite noisy at 2700 with vibration and nowhere near hull speed. Enginge sounds much smoother and happier at 2300 rpm. The engine is a replacement - original was a 21hp 3 cyl I believe and this is a 30hp 4 cyl, so I think it would have an easier time at lower revs.?? Geoff - you mentioned black soot on the transom. I'm interested in this as mine has the same. I've been running it at 2700 because this is what the previous owner told me they were told to do by the mechanic. What I'm curious about - could the soot on my transom be from over revving? I'm hoping I will drop the soot down when the engine revs drop from the pitch change. The engine has just over 1000 hrs and there is no visible black smoke coming from the exhaust.

many thanks,
Steve Gabbott
Vancouver
 
u079721

u079721

Contributing Partner
Interesting discussion

I was interested in Tom Plummer's comments about an alternate method of setting the correct pitch, but I worry about putting it into practice unless you KNOW the exact speed that should be attained at cruising rpm with that engine. In my case we never have reached hull speed of 7.4 kts at cruising revs - it takes full throttle. Crusing revs of 2400 gave us about 6.6 to 6.9 kts. So if you were to use Tom's method you would over prop the engine, no?

I got my adivce from David Gerr's Propeller Handbook. A bit like reading an algebra book, but very helpful.

As to the soot. Some black soot on the transom seems to be inevitable with Ericsons, and I think has a lot to do with the transom shape, and the position of the exhaust - which curls up the side of the boat before being blown away. We still had soot on our transom even after getting the pitch correct. Before that, when we were over propped it was terrible, with lots of unburned soot coming from the exhaust, classic for being over propped.

As for the tach. What I actually meant to suggest is the use of a digital photo tachometer. This is a battery operated gadget that shines a light onto the flywheel (or whatever). No wires, no contact with the engine. You put a small strip of reflective tape in one position, and it reflects back with each engine rev. They cost about $200, and work from about 5 to 100,000 prm. By now I must have loaned mine out to just about everybody I know at my yacht club for them to double check the calibration of their tachometer. (Aso useful to measure the rpm at the prop shaft and compare with the engine to be sure of your reduction gear.)
 
G

gabosifat

Member III
Diesel smell into cockpit

Great advice regarding prop pitch - thanks everyone who replied. We got talking about soot on transoms & one reply suggested this is common with Ericsons. We were really surprised that with our E35-3 at cruise speed, we get a lot of exhaust which seems to curl up over the transom and into the cockpit. The only time this doesn't happen is when the wind is on the beam. You can be motoring into 15knots of breeze & it still seems to spill up & over. We find we have to open the dodger window to get it to clear. The dog lying on the cockpit seat isn't bothered but we are.

Any suggestions?

Many thanks,
Steve Gabbott
Vancouver
 
T

Tom Plummer

Member III
In my earler post I noted the theoretical hull was 7.2 kts. The only real way to establish hull speed for the boat is to observe the bow wave crest. When the crest of the swell is even with the stern at the water line you are at hull speed. The idea being that if you go any faster the stern will drop into the trough of the wave and the boat will from that time on be climbing a hill. The more you exceed your hull speed the deeper into the water you stern squats. It is theoreticaly possabe to cause the stern to squat enough to take on water. In square rigged ships this was a real problem because of the time it took to lower the sails. Ships would get caught in squalls with too much sail up and sink the ship. Hence the term sailing her under.
 
u079721

u079721

Contributing Partner
Exhaust

gabosifat said:
Great advice regarding prop pitch - thanks everyone who replied. We got talking about soot on transoms & one reply suggested this is common with Ericsons. We were really surprised that with our E35-3 at cruise speed, we get a lot of exhaust which seems to curl up over the transom and into the cockpit. The only time this doesn't happen is when the wind is on the beam. You can be motoring into 15knots of breeze & it still seems to spill up & over. We find we have to open the dodger window to get it to clear. The dog lying on the cockpit seat isn't bothered but we are.


I gave this some thought last season while cruising with a friend on a Morgan 38. His exhaust was also leaving black marks on his hull, and he solved the problem by adding about 6 inches of rubber hose to the exhaust port on the transom. That was just enough to separate the fumes from the hull and keep them from curling up the transom.

So we tried to figure out to do the same on my Ericson. Of course the problem is that the exhaust port is actually under water while at speed, and doesn't point aft, but rather out and down. So you would have to add a very long tube, which turns at a right angle, and to figure out a way to keep the force of the water from pulling the tube out of the exhaust fitting.

Which, of course, we couldn't figure out how to do. Finally we decided that the best thing to do, if I were serious about it, would be to simply move the exhaust to the aft part of the transom, and add a short elbow to the new exhaust port to get separation from the hull. If I knew for sure it would work I might have been tempted, even it if did spoil the beautiful lines of the transom. Of course you would also have to then glass over the old exhaust port.

But since I no longer own the boat I will have to leave this experiment to someone else.
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