Propeller Size Change

Boat Model: Downeast 38
Boat Name: Mundial
Zone of Work: Hull & Bottom
Location: Mundial
Date July 2006
Author Rick Stierer

propsize table

Specs from out of the downeaster 38 manual

I noticed that in the specifications portion of the web site that the propeller listed for the Downeast 38 is a16X11. Not wanting to contradict the original specifications but I had an experience where I had to re-prop. I have a RH Michigan 3-blade 15X15. Due to an unforeseen situation (oh, that’s another story entirely) I had to pull the boat out of the water in the Outer Banks. I happened to run into a new generation prop shop complete with computers and formulas, etc. I gave them the specifications of the boat and then the size of the prop I was using. Their computer program came back as my 32 hp Universal diesel being able to turn a 16X15 prop. So, I invested in a Michigan 3-blade 16X15 (same powerplant) and I was amazed at the difference.

First, the economy didn’t change at all – still running at ½ gal per hour at around 2200 rpm. But, performance went to 6.6 knots per hour. I was amazed at the difference one number could make on the overall performance of this boat – but it did.

I will soon be changing powerplants and going to the new, updated Universal M-40B which puts out around 37 hp. With that modification I’ll have the formula run again and see if I can gain another notch or two and get even more performance from it without putting strain on the transmission or engine.

This performance difference is important for those who plan to do any long-distance sailing and might find themselves in calm areas. It might take an extra day or two of motoring to find some wind and the so the increased speed and economy would make a significant difference over a few hundred mile haul.

Thought you’d be interested in this first-hand information.

Rick Stierer

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