Which wedge?

[beechkingd]

I'm repowering to a 90hp Johnson. I've read that it makes sense to install transom wedges to increase the amount of down trim angle available. Which should I get?

[Inquisitor]

I heard the same back in 2007. I have a 5 degree wedge. Couldn't tell you if it is delivering the advertised advantages. Had no way to do a before and after test.

[Russ]

I'm pretty sure BWY installed a wedge on my motor. You could call them and get their recommendations.

[Starscream]

Maybe these photos will help.

The wedge does the opposite of helping, at low speeds. For long cruises remember to trim up to get the thrust parallel with the water's surface. That makes a big improvement in fuel consumption.

I haven't been able to quantify any difference at full throttle with the motor in the full down position or with it tilted slightly up. That suggests to me that the wedge effect is minor, if any. If I was installing the 90 over again, I'd probably still go with wedges, but only because that's what everyone was doing, not because of any great effect that I've witnessed.



You can kind-of see the wedges in this shot:

[Highlander]

Oh well , Here I thought this was gonna be a plumbing Issue !

J

[DaveC426913]

The wedge does the opposite of helping, at low speeds. For long cruises remember to trim up to get the thrust parallel with the water's surface. That makes a big improvement in fuel consumption.

Really? Never even occurred to me.
Maybe I should not be dropping my motor all the way?

[Inquisitor]

The wedge does the opposite of helping, at low speeds. For long cruises remember to trim up to get the thrust parallel with the water's surface. That makes a big improvement in fuel consumption.

Really? Never even occurred to me.
Maybe I should not be dropping my motor all the way?

Interesting! Now that you point it out, it makes some sense. If trying to extend range (be most efficient) it would make sense to not waste any of the motor's force just lifting the tail of the boat. Using it parallel to the surface would use everything to propel forward. Now that I have this VesselView thing on my motor, I might be able to detect the difference from full down to parallel. The caveat to that is if lifting the tail actually reduces drag more than that lost to propel forward. Interesting experiment. Have to try it out some time.

[Starscream]

I can actually see the difference in lower RPM for the same speed when properly trimmed.

We did a trip this summer through the Lachine Canal, a 4 hour trip from our lake to downtown Montréal. The speed limit is 10km/hr the whole way, and there are loooong straight stretches. I played with trim and rpm and there was a small but clear reduction in rpm at 10km/hr when the motor was level.

Combined with our slick VC 17 bottom, new this year, we burned about half the gas that we did on the same trip last year. Don't know which had the greater impact, but I couldn't believe how much gas we still had left after we got home.

[DaveC426913]

I had always assumed that the best thing for the prop was to keep it away from the surface, where it loses propulsion, so I always lower it fully.

But I guess compromise is the key, right? Between keeping it submerged and keeping it horizontal.