[octane]

Hi,

I have an old 16 foot pontoon with a honda 4 stroke bf15 outboard (1997), the prop on it is damaged, and I can't read the stamping on the prop to see what size is currently on there. and I don't have a tach either

what size would you recommend (is a 3 or 4 blade better for pontoon duty?)

thanks

[Silvertip]

I don't mean to be critical but you have no idea what prop you have currently, you have no tach and you have no idea how the current prop performs and armed with that lack of info you expect us to make a recommendation? I would guess the 15 HP Honda would be under powered no matter what prop you installed. I would also suggest that you install whatever prop you can find with the least amount of pitch. Don't even worry about 3 or 4-blade.

[octane]

I know that there is lots on info missing, and that it's a lot to ask... I should say that I'm more looking into a place to start than a recommendation. I'm not looking for performance, just a replacement from the stock prop.

[Silvertip]

When selecting a prop you MUST look at performance. If the prop you install does not allow the engine to rev within the manufacturers wide open throttle rpm band then that prop is wrong for the boat. Since the engine manufacturer has no idea what boat the engine will be mounted on, smaller engines like yours may come with a prop for a regular boat. Pontoons require a very different prop (generally one with a lot less pitch). So without any rpm information (observed rpm) we (or at least I) am of little help. If I were to take a guess at pitch requirement I would say about 9P. You can measure the diameter of your existing prop but you can't measure pitch. Measure from the tip of one blade to the exact center of the prop shaft and multiply by 2 to get the diameter.

[octane]

I was able to find out that the stock prop is a 9.25 x 8p.

So after thinking about it, I decided I should probably try to install a tiny tach prior to changing the prop.

but looking at the tiny tach web page, I have no idea which one is right for my honda bf15 4 stroke?

(http://www.tinytach.com/tinytach/gasoline.php#)

[branman1971]

I found a buddy who had a handheld timing light with an RPM readout. Maybe you know someone who has one. It connects to the battery and then a clip goes on one of the plug wires.

If you can't find one, I would ask around at local boat shops for a used old tach they have laying around for a few bucks.

[rrhodes]

If your toon is a "Lavey" Fiberglass hull then you need a 9x9 or 9x10 prop.

That is based on an online prop calculator.

[Silvertip]

There are basically two types of tiny tachs. A spark plug in a two stroke engine fires every engine revolution. A spark plug on a four stroke motor like your Honda, fires every other revolution. You need one for a four stroke.

[mthieme]

A two stroke tach works off of stator pulses.

[Silvertip]

Tiny tachs do not work off stator pulses. They work off a spark plug wire. Spark plugs on a two stroke fire every revolution on a two stroke engine. They fire every other round on a four stroke but some can fire at both the top and bottom of a stroke. I don't know if that happens on your Honda.