Dhadley: a question on stepped transoms.

[crb478]

I currently have a 1990 Seapro Center console with a 1975 Johnson 115 on the back. The boat is a flats type of boat with a slight v and weighs 1500lbs with out the motor or fuel and gear. It also has a 42 gallon built in fuel tand and there is usually around 30 gal of fuel in it. It has a 20 inch transom with a 15 degree deadrise and it has a step in the transom that is 6 inches up from the bottom of the v, and sets back about 7 inches into unto the bottom stern area of the boat. It is also about 32 inches wide.

I have learned a lot from some of your earlier comments on stepped transoms and I am trying to get mine set up as efficeint as possible without going broke. I currently have my motor in the highest hole which puts the av plate about 1 1/2 inch above the bottom of the boat. I can run about 30-32 mph at WOT and get about 5400 rpm with a four bladed 13 pitch prop. (the four bladed prop has helped it back up much better that the 3) I feel that I need to go higher and am considering getting either a jack plate or a cmc tilt and trim to mount the motor higher. What is the average height for a boat with a stepped transom? How far below the step does the av plate usually ride? Thanks for any help.

 

[Dhadley]

Re: Dhadley: a question on stepped transoms.

You'll probably need a jackplate to take advantage of the hull design and todays prop technology. I can run my Ultima 4 high enough that the motor will overheat and the prop still stays hooked up. Power trim will be a big help also.

What brand prop are you running now?

 

[crb478]

Re: Dhadley: a question on stepped transoms.

Thanks for the quick reply:

I am currently running a solas amita 4 ,13.25X13. I recently took the factory tilt and trim off so I could raise the motor to the top hole and didn't know if I could just mount the motor higher on a CMC tilt and trim unit or I had considered fabricating a manuel jack plate. I really do not want to much set back, but I would love to pick up a few more mph and rpm's. I am hoping not to go high enough that the motor overheats, but with the step it is obvious that it can go higher than those boats without one.

 

[Dhadley]

Re: Dhadley: a question on stepped transoms.

Yes, you are correct, that's the whole theory behind the stepped transom. If your trim was working OK I'd put it back on and get a Bob's manual 4 in 1 plate. You can set it so there's minimal set back - about 2.5" or the full 5". At least that will give you some easy adjustments to get it dialed in.

 

[crb478]

Re: Dhadley: a question on stepped transoms.

The tilt trim motor quit working, but it was still under warrantee so I have a brand new motor I could hook up, but the TT is the 73 - 77 type and while the cylinders seem to be in good shape this will be the 3rd motor I have had on it so I don't have a lot of faith that it will last for years and be trouble free. Thats why I was considering the CMC unit, I could probably sell mine and nearly pay for a brand new unit, especially with the never used arco motor. I do miss the tilt and trim though I know it will run and handle better it on. I also have access to a machine shop and a scrap metal yard so fabricating a jack plate should be more a matter of time than having to spend too much money. Thanks for the advice as I am still kicking around ideas and really value your opinion. How far is the AV plate on your boat below the step in the transom? Mine is currently about 4 to 4 1/2 inches down. How many rpm's and mph do you think are potentially left in my boat assuming I can get it set up right. Thanks again.

 

[Dhadley]

Re: Dhadley: a question on stepped transoms.

Depending on which prop I run the AV plate is even with the step to about 1.5" down. It will run higher but the lower unit doesn't pick up water correctly. There should be some more left in your set up but another thing is the gearcase shape on those older motors. The newer ones are much better.

 

[crb478]

Re: Dhadley: a question on stepped transoms.

Thanks, I will probably try to raise it up a couple of inches and see how it does. I know that the gear case is holding me back some, and I am keeping an eye out for a 115 - 140 looper, but around here they are commanding high prices even for some that are junk and do not run. This motor has been good so far and as long as it keeps getting me where I want to go I can be patient. I may try to pick up some aluminum angle tomorrow from the scrap yard. Then a little milling and welding should get the motor a little higher. Thanks Again. I have no doubt that you have forgotten more than I know.

 

[Dhadley]

Re: Dhadley: a question on stepped transoms.

A V4 looper, now we're talking!

Keep us posted on your progress.

 

[crb478]

Re: Dhadley: a question on stepped transoms.

Ok just checking back in I made a jack plate and ended up with about 2 3/4 inches of set back and found the sweet spot to be about 3/4 inch higher than I was before. I still just have the motor leveled with the keel and using my gps this time top speed was 30.6 mph and wot got to 5400rpm. Average top speed into the current was 30 mph and 52 to 5300 rpm. Not exactly the results that I was hoping for, but with an older motor that may be all she has in her. Ideally I would like to get to 35 to 38 mph and I am still keeping my eyes out for a 115 to 140 looper. I do feel that I have this set up maxed out, If I put the tilt and trim back on I could probably gain a little, but not too much. Right now the motor will cavatate in full turns at full power, but not at all under way. Thanks for all your help. It runs good, but just about like everyone else I always wish I had more speed.