Hello, I recently purchased my 33 and put a new Nanni N4.38. A 37.5 hp 4 cylinder diesel propulsion engine. I have a 3 blade feathering prop. After the installation of the new engine when I take my hands off the Bestwheel, the boat takes a hard right to starboard. After motoring for 45 min to an hour, my wrists were sore from the constant pressure on the wheel to keep the boat going straight.
I had a 30 hp universal prior with the same prop, I don’t recall the boat pulling like this at all.
Was the shaft pulled or re-aligned during the installation? Strut could be bent or mis-aligned. Happened on mine, the strut bolts were bent and that allowed the shaft to be too far to starboard causing excessive tendency to turn to starboard. Excellent prop shop fixed it all for me. : -)
Ron’s guess sounds pretty plausible to me – certainly worth checking out.
A longer shot, but since I see you’re not getting many answers I’ll throw it out there: is there any chance that the new engine’s shaft rotation is opposite from the old one? If the old one called for a righthand prop and the new one requires a lefthand prop, I could imagine that a feathering RH prop might behave oddly.
I used to have a catamaran with twin engines set up to counter-rotate (i.e., one was RH and the other was LH) in order to avoid prop walk. When overhauling the folding props, my diver once accidentally swapped them, installing the RH prop on the LH shaft and the LH prop on the RH shaft. This had the effect of turning forward gear into reverse and vice versa. Unfortunately, I didn’t figure that out until after the confusion led to $6000 worth of collision damage between my boat and the one in front of me on the end tie.
So, things that could never happen, do. That’s why I bring it up.
Mine does it, too. The engine and V-drive are mounted at an angle to the centerline of the boat to facilitate removal of the shaft without first having to remove the rudder. Our rudders are large for the size of the boats and so the cockeyed prop can push pretty hard on them. It’s not a stretch to assume that more HP will push harder.
Poking through the internet, it appears that a Westerbeke engine (common to Nonsuches) runs in a CLOCKWISE shaft direction. A Nanni engine (darn good French engine - common to French, European boats) seems to run in a COUNTERCLOCKWISE direction.
Ah … les Français.
PLEASE - triple check all of this but Capt. Neches may, indeed, be correct. THAT little issue would make that prop pretty crazy.
Interesting. The OP said the prop was not changed with the engine. So maybe the gear lever cables were “reversed” or the gearbox corrects the rotation to clockwise at the shaft? Otherwise they’d have to put it in reverse to go forward and I think that would be more annoying than a pull to starboard.
I’ve had that problem delivering boats and most times it turned out to be a foul bottom. Last year I delivered a 30C and it pulled terribly. After the bottom was cleaned, that problem went away. Beats me!!!
Joe Valinoti
S/V iL Gatto NS30U #221
Sea Harbour YC
Oriental, NC USA
Oops, Brian is right. This is the second retraction I’ve had to post in the last couple of days. So, despite the moniker that Ernie gave me, I’m closer to a sea-monkey than a Captain. Prop shaft rotation direction would change forward to reverse rather than creating greater prop walk. If the boat goes in the direction it’s supposed to, then either the rotation’s the same or appropriate adjustments have been made.
I’d noticed a tendency of both my 26’s to pull to starboard under power with Westerbeke diesels, although not to the extent that you’re describing. But, now that I think about it, the tendency was greater on my first N26, which had a 21 HP, than on my second with an 18 HP. And, having now switched to a lower HP but higher torque electric, the tendency is a bit further lessened.
But, everyone’s suggestions about possible causes (except mine) sound plausible, so it still might be one or more factors contributing: misalignment, bottom fouling, or engine power.
Okay, that would explain it - I thought it might have been some sort of weight distribution issue, but if there’s angle on the shaft to clear the prop that would certainly do it - thanks!
Something else which causes a boat to pull is the flow of the prop wash over the rudder. Because of the downward angle of the prop shaft, there is a different angle of attack of the ascending and descending prop blades as they rotate. This causes a difference in outlfow between the two sides of the prop disk and puts a higher pressure on one side of the rudder. I am not sure that changing the engine should change this behaviour on your boat, however it may be possible the two engines have different torque curves which yields higher torque at the same RPM on your new engine.
Peter Moodie
Nonsuch30U Catalyst #366
Sidney, BC/Winnipeg, MB