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Old 05-06-2020, 08:47   #46
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Join Date: Apr 2015
Location: Sidney, BC and Calabogie ON, Canada
Posts: 143
Re: Maxprop Cutlass bearing Low RPMs

Hi, when your max prop was dissembled, the yard workers/technicians had no knowledge of a max prop and did not bother to find out. Do not go back.

Meantime, your max prop is set way too coarse. The reason you are not getting expected RPM is simply because of that. Unfortunately, as you advance the throttle hoping to get more RPM, because of the coarse setting, your diesel does not have enough power to turn the prop at normal RPM. As a result, you are unknowingly over-boosting your engine which results in excessive cylinder head temperature and possible valve damage. In short, unless you reset the max prop, you will if not destroy your engine, seriously reduce its life.

Thus at the earliest possibility you need to haul at a competent yard and get the prop reset First you need to identify the correct settings. Check with the factory, they will ask such questions as prop diameter, engine power etc. The handbook has this stuff in it. As an example, my 18 inch thee bladed MaxProp is driven by a 50 HP diesel through a 2.62 to 1 reduction ratio, Hurst transmission. Shaft is 30 mm. The settings I use are:
X=K, Y=E (20 degrees). It is a tad coarse and I could operate at 18 degrees. The yacht is a Beneteau 440

Bottom line: fix it now before something breaks like the engine or tranny!
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Old 05-06-2020, 14:49   #47
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Re: Maxprop Cutlass bearing Low RPMs

I agree with the others here that your most likely problem is incorrect pitch setting. I have two of these propellers and know how difficult it is to reassemble them, especially with only two hands.

However with Yanmar engines there is another cause of low revving as you describe and that is coking in the exhaust. The gooseneck of a wet exhaust is the usual site of the problem. Engines running below 2600rpm regularly will build up carbon and block off the exhaust outlet. The engine will rev with no load but will be limited in engine speed once the yacht is in gear.
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