We have finally found a windless day with flat seas in which to test our new props. What we know so far is that at a little over full payload we can achieve 2400RPM at wide open throttle. Our original target was 10.5 knots at 1600 RPM, at three quarters payload. Lets see how we did on the calculations:

The table above was computed using GPS speeds running on reciprocal courses, to eliminate any tidal current effect.

The first item is the target at 1600 revs, we are off by 100 RPMs. This is partially the result of the heavier payload but more on the final prop design. At the very end, after giving the prop specifications to Premier Propeller, we chickened out and backed off the pitch a bit. You can see this in the top RPM at wide open throttle now reaching 2400. Although the logic for being more aggressive was sound, replacing two engines early because of overloading is a costly exercise.

We are pleased to see that our two little 150 HP diesels are still capable of 13 knots with the boat at full load, a speed length ratio of 1.45,  about which we are not going to complain.

We were concerned with reduced tip clearance and noise. This has not been a problem, and while there is no scientific means of telling, these props feel about the same as the previous four bladed wheels of smaller diameter.

We are  getting used to running slower, so far between 10 and 10.5 knots compared to our previous 11. Whether this continues remains to be seen.

Now that we have accurate speed data at various RPM we can take the next calm passage and test fuel burn. In theory we should be a little more efficient.