Honda 75hp Spare prop size

[Kelly Lynn]

What pitch does anyone recommend. I have 13.5X15 right now and I am looking for a spare prop should I get the same or something different. I am running about 4500RPM at 20 to 22 knots.

[thataway]

What is your wide open throttle RPM (and speed). This is the one most significant number for prop selection. You want the engine to meet its rated RPM (5500 in this case I believe). Often people will go down 2" in pitch for the second prop--the reason is that is a good choice for lakes at 3700 foot elevation. Also if you run a heavy load at times--the lower pitch is a good choice.

[Kelly Lynn]

This past weekend when I was at full throttle I was reaching around 6000 RPM's. I would back off the throttle in order to reduce RPM's. Also I have notice one time or another as that my RPM's were erratic for a second, sometimes going to 7000 RPM's. I am not sure if this is the gauge or motor. The motor did not sound any different during the fluctuation.

[Les Lampman]

The 15" pitch prop is usually ideal for the Honda BF75 on a CD22, there's really no reason to get something different unless you're looking for a different result. It sounds great the way it is.

Les

[Kelly Lynn]

Thanks for the input I am going to go stainless 13.5X15.

[Les Lampman]

Unless you need the stainless prop for your area or honestly "you just want it" I don't recommend them. I did extensive testing on the BF75/90 with about every prop I could get my hands on years ago and I could never get any better performance, shifting, economy, or anything else from the stainless prop. Especially as a spare I would just grab a Honda 58130-ZW1-015AH aluminum prop and call it good (weighs less and cost a whole lot less!).

Les

[thataway]

If you are hitting 6000, then you do not want/need to go down in pitch. Go with the 15" back up.

There are some places where the SS prop is a plus--mostly where you may go thru sand or mud on a regular basis. The SS props keep the edges. However, they can also take more abuse, which does not saccrifice the prop, and end up with damage to the shaft or gears.

On my 22 and 25 I had Aluminum props. The Tom Cat and Caracal I have SS props. These are more specialized boats, and the SS prop does add to the performance.

[Tom on Icarus]

I too have a 22 cruiser with a honda 75 and I have been trying to find the right prop too.
I had a 3x13.5X15 and I liked the speed it gave me but at WOT all I could get was 5000 rpm. The Honda owners book says it should be 5000-6000. I was afraid my performance was not really optimal so I had it repitched to 14. That fave me barely 200 more rpm but less speed.
I would say that I am usually not traveling light.
I had my mechanic check the tach and carbs and all is ok.
Do you think it is harmfull to have such a low WOT rpm?

Cheers,
Tom

[Les Lampman]

Hi Tom,

You must have a very heavy boat to only be able to attain 5,000 rpm with a 15" pitch prop. I'm assuming that's an aluminum prop and maybe a standard Honda prop? I've never had to drop to a 13" pitch prop before (on a 3-bladed prop).

So here's the thing about the rpm. Max torque on the BF75 occurs at 4,000 rpm. Max horsepower occurs at 5,500 rpm. So if you can only get to 5,000 rpm at WOT then a couple of things are happening: 1) you can't get 75 hp out of the engine (ever) since that doesn't happen until 5,500 rpm and you really should (for longevity) run the engine at much over 4,000 rpm for extended periods. Since you're just at max torque at 4,000 that's not too bad but there's not much wiggle room there. The general rule of thumb is to cruise no higher than 1,000 rpm under max WOT rpm with the installed prop.

Basically, if you can only get (say) 5,000 rpm out of the engine and you're cruising at 4,500 rpm you're lugging the engine and working it hard. This is akin to climbing a mountain road with your car and leaving it in top gear with the accelerator on the floor. By changing to a lower (flatter) pitch prop you're essentially "changing gears" to a lower gear to let the engine work less hard.

What I usually try to do is prop the BF75 to turn up to around 5,500 rpm to get to all the available horsepower and then you can run the engine up to about 4,500 on a continuous basis if need.

Don't assume that a lower rpm always equates to lower fuel burn. Dropping to a lower pitch prop will raise the rpm for any given speed but it will also decrease the load on the engine and in many cases the economy doesn't change, and in some cases it actually gets better.

My goal is to get a prop on there that best suits the characteristics of the engine and allows it to do its job as well as it can. And that means get the engine to operate in its most efficient range.

Most of the time the Honda 58130-ZW1-015AH (3-bladed 15" pitch) prop will push the CD22 at about 14 knots when the rpm is around 4,000. Going to 4,500 rpm is no big deal and that usually sees about 16 to 17 knots in speed.

Les

[Tom on Icarus]

Les,
Thanks for your detailed reply.
I usually cruise at 4500-4600 rpm. I don't think I am too much heavier than most fisher/cruisers but I do carry a 75 pound dinghy on top.
Have no idea of the make of the prop but yes it is aluminum.
I bought a 4 bladed 13.5X15 honda prop but the WOT was similarily low so I had it repitched to 14 as well. It now gives me around 5500 rpm but cruising speed is pretty slow.
Wish I could get the results others are getting.

Tom

[Les Lampman]

Not trying to be the bearer of bad news here at all. However, you're running the engine pretty hard if you're cruising at 4,500 rpm and can only get 5,000 rpm at WOT.

My best friend has a BF75 on his 1996 CD22. The boat is always loaded and ready to go (so isn't light). We typically cruise at 13 knots at 3,800 rpm (just cause he likes the sound of the engine there). About 4,200 will give us 15 knots and about 17 knots at 4,500 rpm. Right now we've got a 4-bladed 15" Honda prop on there because it "feels good" but it won't get much over 5,000 rpm at WOT. That's ok because he's almost always at 3800 to 4000 rpm. I think he should change to a 3-bladed 15" prop but he's too happy with what he has to make the change.

Les

[louxwe]

I know this is an old thread but it applied to my situation so I was wondering if you all came up with any answers. I recently had some folks do 500 hr maintenance and am having similar problems. At WOT, lever smashed all the way forward, I am barely getting 5000 RPM and maybe 19-20 knots... running 13.75 x 15 3 blade... seems like I used to get 5800-6000 RPM and run 24 knots... shop guys just said well its just an old engine and thats the way it is. Considering dropping to 14 or 13 pitch to see if that helps the RPMs come up. Running on upper end of throttle, 4800-5000 RPM it just feels/sounds like the engine is really chugging but not moving as fast as it should. Shop guys took apart and cleaned carbs, and checked throttle cables and they said it is getting the right amount of fuel.

Is it possible that the engine just has lost that much horsepower fairly quickly. It only has 500 hours so its not really that old? If so would it be wise to go with lower pitch 13-14 to get the RPMs back up higher?

I run in the bays and gulf of mexico... typically it gets really choppy/windy in the afternoons so I cant really run more than say 14-15knots in the afternoons getting back just cause it pounds like hell. But early in the morning esp in the summer it is usually very flat and low winds so I like to go a bit faster to get out into the gulf area quicker but it just seems to not go as fast as it did before the shop worked on it.

Most folks have a BF90 HP on their 22, just wondering if the 75hp is just too small to expect much more than 15 knots, also when I have 3-4 people on it just seems very underpowered.

Thanks