Transmission ID in Fish

I need some help identifying the transmission in my 1987 Fish. The boat was repowered in 2004 with a Kodiak marine Chevy 350 and the prop rotation is now left hand. The transmission seems to be operating fine but I am not seeing the speeds I expect to see from the boat. The engine runs excellent and only has 280 hours on it, so I don't think it is a power issue (it is rated at 290hp).   The prop is an OJ 4 blade LH 13x13 and I am only getting about 17-18mph at 3000 rpm.   I suspect it is the original transmission in the boat simply because it is covered in rust (it was in saltwater for most of the last decade). There is a tag on the top port side of the transmission but I am not able to make out what it says because of the rust. Unfortunately, I don't have any pics of the transmission to post right now, but maybe someone can give me clues as to what to look for to determine what it is?

Behaving overpropped, but not enough to explain everything.

Needs rpms to make the rated power, you are probably receiving only 180 hp at that rpm

To clarify, Rotating the pump housing itself doesn't change the output direction, it simply makes the transmission actually shift when one chooses an alternate input direction

I think you have some compounding issue with state-of-tune as well

Is the boat dry, or is flotation foam possibly saturated? Is the boat loaded heavy with stuff?

You could be looking in the range 14x10 or 13x11, depending if you run light or heavy, but i think a 13x13 doesn't entirely explain your numbers yet

Mechanical advance stuck? see if it operates freely

Well that's a horse of a different color all together. The assumption was that you were giving us WOT performance numbers. If you are limiting the performance to 3000 rpm then there isn't much to be learned from your speed at that point. Its likely a 1:1 borg - no reason to think different. Its rusty so its not a 1.23:1.   It doesn't have a big block so its probably just the plain ol garden variety transmission. See how much it will pull the 13x13 at WOT then come back with that information for a propeller recommendation.   If it were a 1.5:1 it would be long and heavy.   Google borg warner velvet drive 71c and see if you find a picture of your transmission.

Thanks all. After looking at your pictures and some research on the web, I am pretty sure it is a standard Borg Warner Velvet Drive 1:1.   I am curious if there is any good test to determine any transmission slippage I may be experiencing and/or condition of the transmission?   The fluid doesn't seem to be burnt but they could have changed it before I bought it.   I haven't taken it up to WOT just yet as I made a temporary fix to the shaft log that I intend to fully repair this winter. The alignment of the engine was off enough that the shaft was touching the log and apparently caused the log to corrode (the weaker metal), causing a leak condition. I think my sluggish performance at lower rpms is either the propeller or a slipping transmission, or a combination of both. Your recommendations are much appreciated!

Brian,
WOT RPM will tell lots about what's up and if a prop change is needed.

You mention the engine wasn't aligned with the prop shaft but what about the strut? Alignment starts at the strut first so the shaft is roughly centered in the log. Then the engine is aligned to the shaft.

Baitkiller, excellent idea regarding electronic tach. I will pick one up.

PBrainard - my first thought was a bent strut but I quickly found out that finding a new strut for this boat is next to impossible. I have another post in the want ads looking for a strut. I believe it is an SA-20 if I recall correctly.   I was able to get the engine positioned such that it no longer touches the shaft log and the transmission to shaft alignment is within .003. It was about .012 when I started aligning.   I now don't appear to have any vibration at the lower rpms.   Cutlass bearing is still in good shape as well. I decided not to do anything more with it this summer because of several short cruises and fishing trips planned and likely will address it futher this fall/winter.

Ok, thats 'splains a lot. We thought you were wot at 3000rpms.

I suspect your trans is not slipping at all. If it were, you would have other symptoms real fast because that power loss would manifest into big heat, smells, glazed friction disks, and warped plates causing dirty neutral.

I run the exact same same prop in my light tourney boat, nibral oj 4-force. 13x13
, so i can add some relevance to this scenario.

When i mash it, i get instant 3000 - 3200 rpm and rising, almost a slingshot . Its not cavitation, just high slip. Like a high-stall converter would do. Its a kick in the pants. However, its in a much smaller boat, so the effect is, well, exhilarating.

Now, I can extrapolate what this prop would do pushing that large mass you have, and thats a substantial amount of slip, especially at the lower speeds. hmmmm.

This oj prop spead the propwash into a wide flat spread, that almost eliminated roost and flattened wake, so it am very happy with it being a slalom junkie, not getting hit with a glob of 36 mph water to the blsack i got with the acme.

I think a 4 blade ACME 13x12.5 like the #209 would suit your situation well. It has much less slip at slow speeds, less aggressive cup, and a more linear 1:1 krpm-mph curve, regardless of loading, where the 4-force looks increasing hyperbolic with more loading.

I observed this acme would create a comparatively narrow propwash and likely a higher roost, but that is not a factor for you.

I may have some terms wrong, and I agree its a bit soon to choose a pitch without WOT knowledge.

However, that said, even WOT numbers with that particular OJ, will be almost worthless to choose a pitch from the acme line.

I will stick my neck out there and may be the first to advise, in this situation, get a different prop sooner than later. you have a good prop, just not for that application.

You can also get the 3-blade in 1/2" less pitch increments,

The 13x12 and 13x11.5 Acme's are common replacements for the 13x13 hand finished props on 18-19' ski boats... i would suspect that a 23' fish could drop down even more in pitch... 13x10.5 maybe? Like you said, need some baseline performance numbers with the current prop to be sure.