Odd problem at speed

[Clint KY]

The addition of a larger motor has shown an odd problem.

Starting at about 17 - 18 MPH my 25HP on my 1648 throws spray up and out from the motor.
On the diagram the red arrows. The spray is up and out and very close to the transom. It would not be a problem except for the bracket of the trolling motor (the box on the left side of the transom).

The spray hits the bracket and then sprays into the boat. Not a lot, but it does.

I have changed the trim of the motor through the whole range, with no improvement or worsening.

The motor is a little low with the cavitation plate about 1-3/4" below the bottom of the hull, but can not be lifted any more without some sort of a jack plate.

Is the position of the motor causing this, or is there something else for which I should look?

 

[surfman]

What’s the spray coming off of? Can raising the motor fix it? If it can then I would do it in a heartbeat. Can you see over the back when underway?

 

[Clint KY]

surfman » 06 Aug 2014, 12:12[/url]"]What’s the spray coming off of?

I don't know.

surfman » 06 Aug 2014, 12:12[/url]"]Can raising the motor fix it? If it can then I would do it in a heartbeat.

I raised it this morning as much as I can by adding a block under the top of the mount. It takes the clamping screws as close to the top of the transom as I am comfortable running it. I will test it Friday morning to see if 3/4" made any difference, but I am not holding my breath. Any higher and I will have to build a jack plate, which I will if I have to.

surfman » 06 Aug 2014, 12:12[/url]"]Can you see over the back when underway?

Nope - I can't lean over that far and still be able to drive the boat. I am going to try to get a friend to go with me and have him try to see where the spray is originating.

 

[slimpikens]

I had this same problem i raised the motor up with a piece of 3/4 stainless tubeing works perfect now.

 

[lovedr79]

mine does it if i trim my motor down too far.

 

[Clint KY]

slimpikens » 06 Aug 2014, 14:01[/url]"]I had this same problem i raised the motor up with a piece of 3/4 stainless tubeing works perfect now.

I put a 3/4" piece of hardwood between the top of the mount and the transom so I am hoping it does the same for me.

lovedr79 » 06 Aug 2014, 14:20[/url]"]mine does it if i trim my motor down too far.

I tried all 4 holes in the mount to see if it was caused by or affected by the trim. It was the same at all angles. It took a little longer to get up on plane in the bottom two holes, but nothing affected the amount of or the speed at which they spray started. And it did it with two different props. I thought my first prop was the culprit as it had some dinged blades. I got a new (to me) prop with a slightly higher pitch (10" vs. 9") and it had no effect.

I will take it out Friday morning or maybe Thursday afternoon and see what happens.

 

[Johnny]

Clint, ironically, I have the same problem. I took it to the local boat place
and he said it could not be fixed without raising the motor way up on the transom.
This is the alternative he suggested - - - Been running it this way 4 years now and although
it is unsightly, it does fix the problem.

.080" aluminum plate, cut to size with a jig saw. (Lowe's)
1/28 x 1" "Truss Bolts" bolted through the bottom with caulk to
prevent leaking. Thread Lock on the nuts, then cut the bolts off flush
with the nuts. The Truss Bolts are different than the regular
Carriage Bolt - - the head is wider and more flat. Perfect for
use on the bottom of a boat.
I think I got them at Lowe's or Ace Hardware.
Then, I put the metal tape over the leading edge - just because
I had it on hand. (and it is out of sight)

it works for me

 

[Clint KY]

That is interesting. One of the things I thought might be causing it is on my boat the Original Owner replaced the transom wood at some point. He drilled the rivets out of the brace that runs from the floor to the transom and replaced them with screws, inserted from the top with nuts on the bottom. I was going to replace them when I redid the boat, but since they don’t leak, I was not in a hurry. I wondered if the nuts (3) on the bottom could cause enough turbulence to cause the spray. I guess I could replace the screws with the ones you describe, add a few more and build the same spray guard as you did. I think it would be easier than raising the motor.

 

[Johnny]

Just as you said previously, My motor would have to be raised up
beyond that "comfort zone".
My father bought this boat new in 1959 and he cut the transom down himself
to accommodate a 1958 Johnson Sea Horse 35hp short shaft.
Eventually, I will rework the transom to accommodate a more modern 35hp Johnson.
Presently, I have a '79 Johnson 25 on it.
good luck !!

 

[Natedog57]

I don't think the 3 nuts are really contributing to the issue.

The cav plate should be very close to level to the bottom of the hull, maybe slightly below or above. The correct height should not have any excessive spray.

I've never installed a "spray guard" on the underside of the hull, but my guess is that it effectively channels water down to intersect the LU at a more "normal" position.

Sometimes the outboard bracket can be through bolted to the transom, even above the safe height of the clamps. Maybe this isn't an option, but I'd try to raise it properly before drilling more holes below the water line.

 

[Charger25]

Not to butt in, a bud of mine has the same problem w/his 14' Lund running a 25 on it. I'll show him the pics you have here Bare_Johnny. I'm wondering if you could angle that plate down a few degrees and make a trim tab of sorts :idea: :idea:

 

[Johnny]

NP Charger - all comments are most welcome.
Clint, my issue is that my Cavitation Plate is more than 4" below my hull bottom !!!
and as the photos show, the spray guard is about 3/4" or so in the down position.

My father cut the transom down in 1959 for the 1958 Johnson Seahorse 35.
It has seen several motors since that motor died.
I will have to live with this set up until I can Dry Dock my boat and rebuild the transom.
My transom is not wood - it is a fiberglass composite material that is as strong as 3/4" plate aluminum
and I only have a few pieces left to redo the transom.
I am thinking it will be just as much trouble to install a Jack Plate. (plus, won't look purty)
Problem is - I used the 5300 to to caulk and adhere the material to the bare metal hull.
I know that it will take a LOT of effort to remove this stuff as it is STUCK GOOD !!!

So this is why I had to install the Spray Guard.

 

[richg99]

I haven't tried it, but I am pretty sure that I read that you can remove 5200 with heat. Might try heating a paint scraper blade and push it into some 5200 (preferably just a trial, not on the boat).

Rich

 

[Clint KY]

I am hoping to get to test mine in the morning if the weather holds.
I did raise it 3/4" so mine is only 1-1/2" below the bottom now.
On the jack plate: It also moves the motor back which in my case is not desirable.
I have seen some transom extensions built straight up and if it comes to that I will go that approach.
Or I may just use it the way it is and come spring let it become someone else's project.
I am seriously thinking of buying a boat that is already set up, running and ready. I am tired of puttzing with this rig. Between the boat, motors, trailer, etc. I spend more time on it than in it.

 

[richg99]

I've been thinking about your statement that "the motor extends four inches etc.".

That must be putting extreme pressure on the poor little transom when you get up some speed. I guess I'd worry more about that than the spray.

Rich

 

[turbotodd]

the motor is too deep.

You can have the transom built up. That is one way to raise it comfortably. Another way is use of a jack plate-basically a mini-jacker or something similar. By doing so, you will have more adjustability; and most of the time when you find the sweet spot, the boat will pick up quite a bit of speed.

 

[Clint KY]

Finally got a chance to take the boat out after raising the motor. The spray problem is gone.
I had built a shield to keep the spray from splashing off the Trolling Motor bracket and into the boat and it was unnecessary. I will remove it when I get a chance.

 

[richg99]

Super good news. Congrats richg9