Hello,

I just purchased a 21ft Hallett with a ZZ502 paired to an MSA surface drive or “tunnel prop” and was hoping to get some information.

I water tested the boat before purchase and haven’t had any time to wrench on it yet. I was able to negotiate the price down, because there were a few issues.

The boat needs the carb tuned and a good overall tune up but overall it ran well on the test drive. The problem is I’m only getting about 3800rpm wide open @ about 50mph. Now I’m not sure if the timing is correct or if the secondaries are even opening. It did look like the throttle cable linkage was able to max out.

At 3800mph foot to the floor I did notice if I attempted to trim up any further than a quarter it seemed to vibrate and get out of the “sweet” spot. The previous owner stated that msa sent the blueprints to a prop builder here in the US for the prop that’s currently on it. He also stated the prop was built for top end in mind.

regardless I would assume that with a healthy 502 I should be able to get more rpm out of it regardless of the pitch prop or trim being all the way down.

any insight ? Thanks !

Update-

I ran a compression test and found 175psi across the board. The secondaries are indeed opening. I checked the timing and confirmed it is advancing to about 34° base is 9°

I’m beginning to think I’m experiencing cavitation when trimming up. The prop is a 5 blade ofx5 15.25” diameter 28 pitch. Not sure if I’m over propped.

the manufacture stated the when the drive is trimmed all the way down you should not be able to exceed around 4000rpm without trimming up.

Vibrations you must to avoid! It work realyy smoth when you do it properly. Now I have no time, later will send page from manualls where it is nice explanation how to balance it. You have probably the same problem like we had and it is long time bad balanced shaft and rubbers on fleyible joint do not keep metal parts in paralel position anymore. But it is possible to do it.
First you need to check conditions of engine mounts. You buy an old boat and in my oppinion it is work with out of vibrations when new. Engine mounts become damaged and old with time and it makes no sense to involve few hours in balancing but at the end you find bad engine mounts. Check this first!

p.s.
Send few empty messages and after this you will be able to send a foto.

Any torque HP curve?