High Altitude Prop.

[ekhunter]

50 HP Honda, 430 Alu. side console, approx 950lb--fuel 2 guys dog and beer and fuel. Current prop. 11.1 inch dia. 13 pitch, 4800 max RPM at 5300 ft elev. Several questions: 1) who makes good Alu. prop. I see a number of Manuf. but not sure who is who--new to this stuff. 2) Some of the inquires I have made--prop. selector sites, suggest a full inch decrease in dia. and near the same or greater pitch while others suggest inch increase in dia and as much as 4 pitch decrease. My normal fishing is at 8500 ft. I would prefer a prop that works well at 5300 ft and accept the loss at 8500 ft or somewhere in between--I will not over rev. at this elevation. In addition, some say that rule of thumb--200 rpm increase per pitch reduction with as little weight as I am pushing may not apply as much and reduce only 2 pitch and test. The motor is mounted in second hole, cav. plate rest approx. .25" up from bottom of the "V"--not the bottom of the keel--prob. 1" up from bottom of keel. Cup on prop. is a whole nother deal. Any suggestions.

 

[steelespike]

Re: High Altitude Prop.

What is the max rated rpm of the Honda?I would guess close to 6,000.
The Turning Point props give stainless performance at aluminum prices.
Unfortunately prop selectors are only as good as their program and the information given.What is your present speed?
I think I would go down at least to 11" Probably only put you at about 5,200 The Turning point prop should allow another hole or so height which may help your performance a little as well.

 

[ekhunter]

Re: High Altitude Prop.

WOT rated rpm is 5500-6000, dealer discussions indicate that this engine LIKES 5700 WOT. On the Turning point site, they recommend a 10.25 dia and 15 pitch prop. I am totally unfamiliar with these props, are they good.

 

[steelespike]

Re: High Altitude Prop.

Assuming your motor is healthy and your present prop is in good shape.
A 15 will further lower your rpm,do to your elevation.What is your rpm and speed with a light load.I think you need to shoot for 5,700 with a light load.
There have been a number of reports here on the Turning Point results people had all very favorable.

 

[ekhunter]

Re: High Altitude Prop.

I will mount my fishfinder this weekend and determine speed, the tach shows 4800 WOT trimed out with just me and my 63lb dog and 6 gal. of fuel. Thats at 5300 ft elev. I will check out the Turning point site. I am thinking that a 11.1 to 11.75 dia and 11 pitch may be the answer. With such a light boat we may see the rpm jump up more than the rule of thumb--thoughts?

 

[hwsiii]

Re: High Altitude Prop.

Ekhunter, can you tell us the gear ratio and year of the Motor, as well as is it a four stroke. What manufacturer and model of prop you have now, as well as does it have much cup and is the cup in the trailing edge or only at the blade tips and is it aluminum or stainless. And what GPS speed you are getting at 4,800 RPM

H

 

[ekhunter]

Re: High Altitude Prop.

the prop is a stock honda 3 blade 11.1 dia 13 pitch It is a 2001 Honda BF 50 excellent shape and I think the ratios are 2:08:1, I do not have gps speed yet, will test this weekend with fishfinder/gps mounted. Most of my fishin is at 8500 ft, I am starting to think that I may have to go to a 9 pitch, max rev down here and acceptable up there.

 

[ekhunter]

Re: High Altitude Prop.

I forgot to say that it is a 4 stroke, as for the cup, I don't know. I am fairly certain that is a Solas prop though.

 

[hwsiii]

Re: High Altitude Prop.

Steele you are real close on the RPM change. If you use the same manufacturer and model you have now Ekhunter and drop to an 11" pitch you will be turning right at 5,400 RPM. If you go to a 9" pitch you will be turning close to 6,300 RPM, which is definitely too high. But if you change models of props I can't really say, because changing the geometry of the prop messes up the calculations.

If you change to a 10" prop this is what you can expect

H.

 

[ekhunter]

Re: High Altitude Prop.

Perfect, that is very helpful information, thank you. In an effort to prevent over rev., I watch my tach pretty closely anyway, I think the 10 pitch, Solas/Honda may be the right selection. That will keep me at the proper RPM range at 5300ft elev. and provide acceptable performance and engine longetivety at 8500 ft, where I fish most.

 

[hwsiii]

Re: High Altitude Prop.

PLease post your results, so I can enter them into my database, I would appreciate it very much.

H

 

[steelespike]

Re: High Altitude Prop.

Have you given any thought to rejeting or have you allready done so?

 

[ekhunter]

Re: High Altitude Prop.

Went fishing last few days at 8500 ft. I put a Michigan Match 12.25X10 pitch on the Honda 50. Hull weight, 430 dry, Me 205lb, plus 100lb gas and gear. I was able to achieve 24 mph and 4500 rpm. Although the engine ran great, trolled ALL DAY at 900 rpm--2.5mph, I think re-jetting will be the answer. I think Honda has jet specs for operation above 5000 ft. It looks like a pain in the but. Do I have to remove the carbs or can I get to the bowl screws and pop in new mains and pilot jets? I will test this set up with stock jets at a local lake--5300ft and post results.

 

[steelespike]

Re: High Altitude Prop.

If you run at higher elevations I think a rejet is the way to go.
Sorry I can't help with the procedure but post in the Honda forum
someone is sure to know.