More 25 express prop talk. (New prop)

[Howesounder]

I tried a 4 blade 14 3/4 diameter 15 inch on the boat today as is was a very inexpensive experiment.

While the 15.5 17" 3 blade stainless would not let the boat go below 20 without troublesome loss of grip from time to time or over waves, it was solid over 22 knots, never loosing grip until sharp corners.

The 4 blade 15 pitch is solid as hell up to 22-24 knots, and above that it looses grip, and won't really let the boat go any faster. As low as 13 knots, even silly boat high attitude it just does not loose grip, and same for corners.

So these two props seem to create the polar opposites in performance. For this year I will use this 4 blade, and look for a 30 inch engine or spacer kit for next year. Thanks for all of your thoughtful comments and encouragement.

Steve

[Bo Toepfer]

Thanks Steve Great data,, did you happen to record the RPM"s,, any protest in steering? if I recall you are running a 25" shaft,, if possible when I get to that point I think I will look for a 30" shaft,, although I have a 200 HDPI with a 25" that I can use! any fuel usage data ?

all thoughts welcome!

[Howesounder]

I don't have any useful fuel data, but I am going to fuel up this week, so will have pretty good numbers, as I know to the yard how far I have gone since being careful to fill both tanks to the top last week. I will report in on that in this thread later this week.

As for the 25 inch shaft I had a look at that last night on mine. Even if I could drop mine further I don't think it would be a good idea to have either the engine, or bracket any lower. My bracket height was set for twins, and those 25 inch shaft engines would have been fine due to their relative height to the boat bottom off the centreline. I suspect they could even NOT be at their lowest possible setting to keep the power heads out of the water. Mine on the other hand is looking a little too close to the wake when at semi planing speeds. So I think the best setup for a hassle free operation is twin 25" shafts, or a single 30"

Steve

[Bo Toepfer]

Thanks Steve, can you tell me the height t difference between your brackets swim plat form and the curb the engine sits on?

[Howesounder]

Hello Toepfer, height above the swim grid is 2.5 inches.

Tried my new planing plate last night. Removed the store bought dolphin that helped a bit, and installed the 1/4" aluminum plate I waterjet cut with a slot and beveled and angled leading edges. It's an enormous 32" wide, and 18" long. Still have the 4 blade on. The boat stays completely bow down from idle to 4-6-8-10-12-14 knots, and the boat is on a solid plane at 12. At 10 the wake has cleaned up, but there is a lot of spray off the engine still. The boat now "needs" the engine to come up to get the nose up a bit, as otherwise it ploughs, but interestingly, the speed only rises 1-2 knots when you raise the bow. (Makes a much bigger speed difference at higher speeds) Could not get the prop to loose grip in turns or waves etc. At 22 knots the plate is clear of the water except a little bit of the trailing edge end. At 24 knots it is free and clear of the water. From 14 knots and up it is on a very solid plane with a pretty wake. Having changed to a 15" pitch, 4 blade prop, I suspect that it will now hold its speed well in chop, wind etc at these lowers speeds, where before it was a royal pain in the ass to hold at any speed below 20. So a complete sucsess I think. Fantastic low speed performance, with zero drag to the boat at above 22 knots.

Steve