I’ve had a hard time finding a decent RH crescent #3. I grenaded my lower- it’s destroyed. I’ve been using #6 prop shafts in these units. The previous owner went through 4 drives in 4 seasons. I’m on 2 now, in 2 seasons. Powered by Merlin 588 blower motors making just over 850 on low boost (3-4).

ive been talking to a guy about converting the boat over to #5’s or possibly 4’s. His thought was with a #5 stacked spacer 2” + 1” the X dimension would be 2” higher than current set up, gaining top speed and obviously a stronger drive. I know I’d sacrifice a bit on plane out but that’s what 380’s are for!

anyone ever done this swap on a straight bottom GUN? Mine is a 89’ LipShip. Any input is appreciated!

- Bill

Hi Bill , I converted my 38 flat deck from 3’s to 5’s . And in order to avoid buying boxes and The rest of the equipment I put a notch in my hull . Check out a thread “ How to put a notch in a flat deck” . I run the drives 2 and 1/2 Inches below the deck with 3 inches of spacers . Planes in 5 seconds at 3000 rpm and runs 76 mph with the wrong props . I am going to take out an inch of spacers and some different props . Good luck . Rick G .

how far below the bottom are your current drives?

Thanks Rick. Did you gain any mph?

Good question. I will get an exact measurement...

I have 2" spacers and I have 2 LH drives , 19 and 26 spline fyi.

I have a fair amount of experience on this one.

1990 Gun with notch. Originally a TRS boat, then to Konrad, then to #5 SSM. Similar power to you, so all should be pretty even.

One thing you may want to seek advice on is that once you start piling up the spacers, sounds like you are going 3" total, this stresses the vertical shafts. May be a non-issue, but it's something I never thought about until it was pointed out to me by another boater / mechanic who works on the drives. I also have boxes, which give me more adjustability. I would say from asking around that on the older non-step heavy guns, you want that prop shaft 1" below the running surface. I was initially setup even, and it took all of an 18" diameter prop to even hope to get on plane, coupled with at a minimum, a 200# friend to climb up in the nose to get it up on plane.

I've tried no spacer ("even"), 1" & 2" spacer.
1. No spacer fastest, but there were times I couldn't plane and if you've ever come off plane in 4-6 footers in a bad area, this can be dangerous and possibly sink your boat.
2. 2.0" spacer, most usable but took off speed on the top end when spinning a bigger 18" diameter prop. I also could not get RPMs above 5100.
3. 1.0" spacer, this is the happy medium, so call the prop shaft 1.0" below the bottom of the running surface. It's still a little hard to plane, but more usable and speed did not suffer as much.

I hope maybe some of that helps to make your decision, also hope it saves you hours upon hours of messing with the setup and hardware changes.. These boats aren't super sensitive speed-wise to the setup, but more of a usability type thing. If you're full pleasure setup, and side by side engines, I honestly don't think there is a whole lot of speed to be gained by going to a surfacing type drive. It's more of a race boat setup and with super high drives, makes these things harder to operate. I would definitely do it again though, and would encourage you to go to a #5 or #6 drive.

Here is the setup.

Good looking boat Frick. I dig the scoops!

im most certainly not racing it. Fun runs, cove outs and bar to bar at LOTO. I’ll never be the fastest, I just want to improve my reliability. After much more research it seems #5’s are only a viable option if used in conjunction with boxes. By the time we get all components and drive line changes sorted I’m up in cost close to m6 swap. Where do you draw the line? I love the boat, it almost paid for and plan on keeping it for a long time.

https://www.ebay.com/itm/Mercruiser-...AAAOSwV-Je5~s6

i saw that. Looks like hell, pitted badly and only description is “turns freely”... not even a mention of gear ratio. I’ll pass but I appreciate the heads up.

http://ebay.us/wXf7BB?cmpnId=5338273189