Problem with leg too long - where should it sit?

[stuee]

Hi.
I had a 100 Merc on my boat where the leg was long and the keel line was half way through the prop,
I now have a 235 Johnson on it with and xl leg which i have another problem.
It works fine in the water but when i get a little speed up it starts spraying a large amount of water and slows me down.

I looked while a mate steered and it looks like the leg is too long now and it sits too lowwhere you can see the keel line, as this area is a large round part thats whats causing the spray.
My 2 questions are...


1, where should the keel of the boat be inline with A b c or D?

2, how would i get the motor high enough as from the keel line to letter a (the first cavitation plate) is 90mm and i only have 105mm from the bottom bolt hole to the edge of the transom?


Thanks for any advice or help.

 

[metriccrescentwrench]

Re: Problem with leg too long - where should it sit?

Well, in the second photo I can see that you have two more holes of adjustment to raise the engine. Just go up one hole at a time and see if that gets the engine to where it needs to be. HOWEVER, from those photos it looks as though you might not be able to get there, even going to the last hole, and if that's the case your two choices are live with it as is or get an engine with the proper length midsection.

Any "rule" about where the keel should be in relation to an engine's AV plate are merely educated guesses. What really matters is that the AV plate should ideally skim along the surface of the water when the boat's on plane, and that's generally accomplished by a bit of trial and error.

 

[stuee]

Re: Problem with leg too long - where should it sit?

thants Met,
i saw it never added the second photo to go with the post. ill attach now that more of an explaination of the line of things.
thanks

 

[stuee]

Re: Problem with leg too long - where should it sit?

So B would be the AV plate and that should almost be in line with the keel?

 

[Frank Acampora]

Re: Problem with leg too long - where should it sit?



Your engine leg is 5 inches too long. It is clear from the photos that there is NOT enough adjustment on the mounting holes. Your anti slash plate is a good 3 inces below the water and it should be about 2 inches above. The Anti-ventilation plate is a good 5 inches below the water line. Not only are you splashing water up the leg, you are losing speed.

You need to raise the transom about 4-5 inches if you want to keep that engine.

Here is a small one I did, but it gives you the idea of what is necessary.

 

[stuee]

Re: Problem with leg too long - where should it sit?

5 inches -- oooh.
to make the letter B to be the same level as the keel on the boat it is 90mm.

I can lift the engine using the mounts and current setup about 80mm, im thinking this will be alot better than the current setup and bring the av plate to only about 10mm below the keel.

 

[stuee]

Re: Problem with leg too long - where should it sit?

Edit.....

 

[Frank Acampora]

Re: Problem with leg too long - where should it sit?

"B" is an anti-splash plate. It keeps water impacting the leg from riding up it and spraying all over, including into the splashwell. It should be above the water line when running. "D" or anti-ventilation plate, commonly called "cavitation plate" should be at the level of the keel or even slightly (about 20 mm) above it. Most start with it even with the bottom of the hull and raise it in small increments.

As I said above, you need to raise the transom about 110 mm.

Look about 8 posts down by maryhannaj "Cavitaiton plate does this look right?" to see the approximate correct engine height.

 

[Sea Rider]

Re: Problem with leg too long - where should it sit?

Hi Stuee,

Is the posted pic the actual engine in current use ? If not, can you post a pic of the current one to check something on lower tail. Used to have same issue with a boat/engine combo, now set at a a perfect marriage.-

Happy Boating

 

[boobie]

Re: Problem with leg too long - where should it sit?

Ever think of getting a jack plate ?? CMC.com makes them.

 

[limitout]

Re: Problem with leg too long - where should it sit?

5 inches -- oooh.
to make the letter B to be the same level as the keel on the boat it is 90mm.

I can lift the engine using the mounts and current setup about 80mm, im thinking this will be alot better than the current setup and bring the av plate to only about 10mm below the keel.

yep go all the way to the last hole and you will be close enough so you shouldn't have any issues. you will still be too low but not enough I think to be a big problem and your only other option is to buy another motor midsection, or get a jack plate for it.

I wouldn't try raising the transom as mentioned earlier because its just too hard and to dangerous if its not secured properly for the strength it needs. I have done it and seen it done and helped others do it and we all agreed in the end it wasn't worth what we had to put into it when its easier to get another motor or swap midsections. the midsection is just an empty shel that connects the lower unit and the power head to the mounting bracket so it has no real mechanical function other then a spacer.

you can shorten your motor fairly easy if you buy a salvage yard midsection and put your powerhead (engine block) on top of it then you just have your lower units main shaft replaced for the shorter one and you now have a short shaft motor. this is a much better and in the long run safer way to do it then adding onto your transom to raise it. just be sure to swap out the numbers plate on the motor so it has your numbers.

 

[stuee]

Re: Problem with leg too long - where should it sit?

ok i will play with moving it higher.
Would it matter the fact the little hook on the top will not be hooked onto the transom anymore?

What i was thinking to do was as the image shows.
As you can see the transom dips where the motor brackets is and had i know this when i rebuilt the transom i wouldnt have shaped it to the shell.

The original bracket mount where it is now is in red and where it i could move it to is blue.


I can get a some 3mm aluminium and have it folded to the shape as bottom whith the outside v shape and the inside to shape of the splashwell.
I do actually still have the 2 peices of 18mm marine ply i cut out from the transom months ago and thinking i can glass them in then put the aluminium cover over it all and bolt where the grey dots are then the top of the alumilium spanning the gap plus 14inch acoss the top each side. the bracket will then hook back on the top and bolt will go through the aluminium / new fibreglassed ply / aluminum and the bottom bolt throught the mid secion on the transom.

Would this be a good move to make and be secure enough?

Cheers

 

[metriccrescentwrench]

Re: Problem with leg too long - where should it sit?

Would it matter the fact the little hook on the top will not be hooked onto the transom anymore?

The bolts support the engine, that "hook" doesn't do anything. Each of those bolts individually has a shear strength rating of many times the weight of the engine, so there's plenty of built in safety factor.

 

[Frank Acampora]

Re: Problem with leg too long - where should it sit?

From the drawing it appears that the modification will be adequate as long as the center is filled with the marine plywood.

If the boat now has a transom cap, remove it and glue the ply to the existing transom ply before you slide on the aluminum cap.

Most times I use 1/4 to 5/16 diameter stainless bolts but in your case, because of the high horsepower, I would go with 3/8 (10mm). Be certain the center bolts are spaced far enough apart that the engine clamps will fit between them. Use extra thick fender washersto spread the compression loads and use self locking nylock nuts.

You can also add two "U" shaped pieces of aluminum inside the transom, over the engine mounting bolts and under the nuts. I don't have any good photos, but if you google youtube Mini Cub Chrysler 60 at one point in the video you can clearly see them.

As with any project: measure twice, cut once.

Good luck.

 

[limitout]

Re: Problem with leg too long - where should it sit?

Would this be a good move to make and be secure enough?

the problem with transom ad-ons is there is never going to be anything as strong as a solid structure going across the back of the boat. once its cut into that section if added back on is not going to be strong or secure and while it may not come off it will not be or act as one solid unit either. you have the right idea in wrapping the area overlapping far enough to give it strength again but in the process you may cause cracks and leaks to allow water to get into the transom.

now that you have cut it your best solution may be to just work with it the way it is but only you know your own skill level and common sense to know whats going to work or not. besides strength you have to thing long term about the seal of the fiberglass not cracking or leaking when pressure is put on it by whatever you build.

if you are going to do it in heavy guage aluminum then use square channel to frame it in and allow solid mounting points for the bolt pattern then weld the outer skin over it keeping in mind most of the pressure will be trying to push the top into the boat during operation so weld the outer skin to the frame then the inside can be covered or left uncovered. when trailering is when it goes the other way and all the force is trying to pull it off of the transom so long angle iron cross braces going over most of the transom would be best IMO.


also as for those "hooks", as mcw mentioned they do nothing and are just there so the motor doesn't fall or slip off the transom in the mounting process, its a temp hanger for safety is all and is a carry over from the days when motors had those screw cups to tighten down.