Basic trim questions for a 25hp Mercury 0C196683 "short shaft"

[wolfee]

Boat: 1980's Sea Nymph Fishing Machine, 16' 6" V-hull

I had to replace the transom a few years back (there's a thread here about it with pic's) and cut the new transom down to a short shaft height to match the old transom. The problem I'm having is I never get on plane, it runs decent but never gets up on plane.

If I have the trim set to the second hole from the transom (current setting), the AV plate is almost even with the keel, maybe 1/4 inch high BUT the AV plate isn't parallel.
If I have the trim set to the third hole from the transom, the AV plate is about 1" above the keel and parallel to the keel. (haven't tried this setting yet)

From searching the web, perfectly inline with the keel is "standard" and slightly above the keel is for more speed for skiing, etc. I just fish, maybe pull a tube for my son but that hasn't happened yet anyway

I also purchased a 4-blade prop that is a breakaway prop (non-metallic) because I read that a 4-blade would get you up on plane faster. Problem is I never get on plane. So I ordered and have a new Quicksilver 3-blade prop (to specs for motor) that I am going to switch back to.

There was a time when I was able to get the boat on plane and it shot around the lake pretty good, but that was a long time ago. (carb rebuild and water pump replacement)

Is there such a thing as a short shaft 50 hp? Everything I search for ends up being 20" or 25". If that's the case. how would I go about altering the transom back to it's normal height? 20" Steel plates?

One more question: Is there a way to put the motor on a jackplate or just a mounting plate for this motor? There's only one hole for mounting and no adjustments for the clamp.

Thanks for any help here, it would be great to get this thing back on plane somehow.

 

[ondarvr]

What pitch are the props you're trying, just being a 4 blade won't help get you on plane if it's not the correct pitch. And there's a very good chance going back to the stock spec prop won't help either, you may need a much lower pitch. You're probably at or below the very low end of the HP range for that boat, so getting on plane could be tough no matter what you do. (when I looked at the spec it said 60HP was the max rating, but I don't your exact model)

 

[Sea Rider]

I'm about to write an essay about this highly missunderstood trim issue as there's to much hanky panky going on here about trim settings, everyone has their own theory about, mainly due for to bad tech approaches constantly repeated by written or word of mouth, in reality no one read what's posted on every outboard, boat brand Owner's Manuals that their respective outboard/boat brand came with..

As this is a complex, & very long to explain issue, might well start reading this post fully to understand how trim and other tech parameters works. Was written for the boating folks across the pond. It's used as first OB/boat installation. Works spot on for any kind of outboard and boat brand, it's a matter to try it.

http://www.rib.net/forum/f50/abc-sib-rib-installation-guidelines-58373.html

Report your findings on what needs to be arranged, modified compared to what's posted on the link, can work from there for better boating.

Happy Boating

 

[wolfee]

What pitch are the props you're trying, just being a 4 blade won't help get you on plane if it's not the correct pitch. And there's a very good chance going back to the stock spec prop won't help either, you may need a much lower pitch. You're probably at or below the very low end of the HP range for that boat, so getting on plane could be tough no matter what you do. (when I looked at the spec it said 60HP was the max rating, but I don't your exact model)

The sticker on the boat says max 50 hp, that's why I was wondering about finding a 50hp short shaft outboard, but everything I see is either 20" or 25".
I didn't think you could/should mess with the recommended pitch for your motor. If I was to try another pitch, can you give a quick explanation. The prop I ordered is "Solas Amita 3 Aluminum 13P Merc". The prop that is on the boat now is the 4 blade breakaway prop that I tried just for kicks.

 

[wolfee]

"Report your findings on what needs to be arranged, modified compared to what's posted on the link, can work from there for better boating."

Thanks Sea Rider, I'll take a look at the link.

 

[Sea Rider]

Max transom 60 HP rated is for max number of passengers say 7 up, if with just a under powered 25 HP-OB can have good boating, but with way much less passengers on board say 2-3 max. For combo to plane need to dial all those mentioned tech parameters while lightly loaded.

Once easy to plane, will need a less pitch prop maximization to pull wot revs higher, will plane faster, for that enterprise will need to install an induction tach and go from there fine tuning combo.

BTW there are lots of 2-4-TLDI OB's in S-L shaft sizes probably not in your area. Tohatsu has them all, a matter to check..

Happy Boating

 

[ondarvr]

There are a few 50hp short shafts around, but not many, so finding one may be tough.

​When you get the new prop see what happens, and a tach is required to get it dialed in correctly.