Does this sound like I have too high of a pitch?

[Albers]

I have a 1993 Wellcraft/Excel 26se cruiser with a VP 5.7 carbureted with SP-C drive with a 1.61 ratio. Loaded weight is 5,800 lbs. Current prop is a 15.5" x 17p Solas 3 blade prop.

My problem is that it takes FOREVER to plane - even using the trim tabs and sometimes even on the way back from Catalina when the current is actually pushing me it is common for the boat to fall off of plane and seems like a loss of power.

I used to have a 15.5" x 15p and that seemed to do good and I could tach out easily at 5,500 + rpm so I thought I'd switch to a 17p to try to get a little better mileage - I didn't have these problems with that prop.

What confuses me is that on the original specs it shows this boat at 38.3 mph @ 4,500 rpm and 25.6 mph @ 3,250 cruise. With either the 15p or the current 17p the fastest this thing can go is around 25 but speed isn't my main goal - I use this on Long Beach to Catalina runs (30 mi) and am just trying to improve the fuel economy. If nobody has any input I was thinking of just cruising there at 7-10 kts and just see what mileage I get that way vs. the current 2 mpg I'm getting now. Should I just be happy with the 2mpg? is that expected for this size boat/motor/single prop setup?

 

[Texasmark]

Re: Does this sound like I have too high of a pitch?

Most cruising economy is just above planing speeds. The hull drag is reduced by the boat being "on the water" and the other economy factors have not built up to sufficient levels to be the controlling factors. Pull up any current mfgr's www and look at performance curves. Note the big efficiency increase just above plane and watch it fall off at the higher speeds.

Economy is a multi faceted question involving the whole system. Sloppy hole shot is usually an overloaded engine due to boat load/design, engine HP availabilty, or props ability to allow the engine to deliver it's HP. Hole shot needs thrust. Thrust comes from large diameter, shallow pitched props, or in the case of bass boats, ported props that allow exhaust gasses across the blades giving faster rpms which bring up the HP faster to spin the high pitched (designed for high speed) prop faster. Cruising speeds, just above plane also do well with this large diameter, shallow pitch type prop because the thrust is there. You can read report after report on here where situations were encountered, props changed and results achieved.

However, on a light, fast hull, this kind of prop will not perform. Also multi bladed props that work well for the above, are less efficient on these type boats....ocean racer cleaver props excepted...different critters. Mercury marine learned years ago that the 2 blade, small diameter, high pitched was the most efficient high speed prop.....aka racing 3 pt hydroplanes. But you aren't interested in that.

An engine that isn't working hard is more efficient. Pull a trailer through the mountains and coast on level ground. You know what the difference is. Boat engine is the same critter. Sometimes, increasing the diameter and decreasing the pitch doesn't hurt your mph. By allowing the engine to reach it's recommended rpm range, the shallow pitched prop spins faster and can make up in rpms for what it lost in pitch. A well designed/applied prop can be more efficient in itself by slipping less. Slipping being defined as the actual boat speed vs the speed that would be achieved by a certain prop in a solid medium....www has a BAM prop slip calculator where you can diddle numbers and see for yourself.

So, with all that blab, larger diameter, shallower pitch, hole shot would improve, control just above plane would improve, engine rpms would come up which always helps and in the long run, you may also get more mpg. Buttttt the big problem is that all this is pure speculation until you get out on the water and test your equipment. Just too many variables.

HTH,
Mark

 

[Scott Danforth]

Re: Does this sound like I have too high of a pitch?

2MG is pretty good. I would try a vented prop to improve your hole shot.

 

[steelespike]

Re: Does this sound like I have too high of a pitch?

What prop was on for the original specs? Keep in mind factory specs are based on the bare boat no 20 year accumulation of cargo.
Its also possible that your 20year old motor may be a little tired.
Speaking very generally your 15" pitch prop usually would make it easier to maintain a cruising speed and not struggle as much with wave conditions than the 17.The 17 might make a little more speed at similar rpm.
I don't think your 5.7 is intended to run at 5500 something more like 4800.

 

[Maclin]

Re: Does this sound like I have too high of a pitch?

This observation will not be much help, but, a boat that large needs a DuoProp.

There, I said it now :focus:

 

[Albers]

Re: Does this sound like I have too high of a pitch?

Thanks guys! I'm going to switch back to my 15.5" x 15p prop next week and I'll keep good track of rpm's, WOT and speed. It sounds like the 17p might be a little much for my boat... and yeah Maclin, I wish I had the duo props...
I see I can get a 16" x 15p prop but does anyone that extra 1/2" diameter do much?

 

[Texasmark]

Re: Does this sound like I have too high of a pitch?

Prop dimensions vary somewhat as a function of the design. So one would really have to ask the prop designer. Obviously large diameter and shallow pitch is for pushing and small diameter and high pitch is for running, but within an area of props of like kind, you will find variances as the pitch changes.

Mark