Boat motor seems to make a huge wake . . . Tohatsu 20hp

[catfighter]

Re: Boat motor seems to make a huge wake . . . Tohatsu 20hp

Looks better but a tighter shot from the side showing where the cav plate now resides as to the boats bottom would help. No big deal though as only your test drive will find out the higher position improves the spray. it will!
PS: don't forget to put that plug back in.

I have nightmares about forgetting to put the plug back in. . . .

Trimming it made it much better without the shim, so I'm thinking this is going to be ideal (it's maybe 1/4" below the keel line now).

I'll take some pictures or video to show the difference from before. I already have a rooster tail just from properly trimming it.


I'm trying to figure out where this motor should be and then I'm going to bolt it down and forget about it.

 

[Sea Rider]

Re: Boat motor seems to make a huge wake . . . Tohatsu 20hp

It's not a matter on how well the shim looks nor the physical distance from AC plate to hull, what you need to do and stop guessing is place your boat on water, trim engine to have a perpendicular motor, place one adult passenger at bow, go for a wot spin and check your back engine water flow, take a picture, film, movie or whatever to check where flow at speed is passing by. 3 conditions to watch for :

If water flow hits upper portion passing small plate, you'll have excesive water splashes at back transom mainly because that portion does not have the triangular shape that cuts water flow. Flow just smashes against, definitely no good, too much tail drag which will slow you down.

If water flow passes slightly under small upper plate, that's the ideal sweet spot, will have good hole shot, good acceleration, top speed and sweet close & tight turns.

If water flow passes slightly over A Cav Plate would be perfect if wanting to race on flat calm waters, on choppy seas and/or close turns will experiment airation, cavitation issues.

Our shop height tunes different boats with Tohatsu engines up tp 50 HP regularly and everybody happy with their excellent performance. This must be done under trial, error and patience, and will need to do it once and forever and ever, amen!!

Happy Boating

 

[catfighter]

Re: Boat motor seems to make a huge wake . . . Tohatsu 20hp

So the motor runs very, very well now! the hole shot is still a little slow but you'll have that with a tri-hull, I suppose.

here's a video:

http://www.youtube.com/watch?v=058ZGQQ7tyQ&feature=youtu.be


that's at 3/4 throttle and I seems to be going super fast -- like I really don't think I want it going any faster! And this is fully loaded with two adults and all the gear needed for a night.

I think I'll leave it like this, unless you guys see any issues.

 

[msaunoras]

Re: Boat motor seems to make a huge wake . . . Tohatsu 20hp

Wow, this is very interesting. I have learned a lot more about boating since joining here. My mirrocraft has a power tilt and trim that I had installed about a year after I got it. This trim raised the engine out of the water atleast an inch maybe more. The setback is an even greater distance. I always wondered why the boat ran so much faster after the power trim was installed.

I went out and took a look at the position of my engine in relation to the transom. The anti-cavitation plate is about flush with the bottom of the boat, maybe a 1/4" higher when the engine is trimmed level (thanks for the tip about the name plate being level)

My engine definitely has some extra spray running at wot. Does this mean it could stand to be raised a little more?

 

[Expidia]

Re: Boat motor seems to make a huge wake . . . Tohatsu 20hp

Msaunora
You probably won't see much of a difference being that you are only running an 18hp outboard. You are only looking at a possible 3/4 of an inch range higher. If you have clamps and it's not bolted down you could use 1/4 inch strips of wood to raise it and then test drive with each height change.

Most outboards that are mounted too low are the ones that drag too much in the water and cause a lot of extra spray like the original posters issue. You are lucky enough to have power trim. Most small outboards don't have that luxury. So you can just tap the trim button and move the cav plate a little higher or lower.

It's not like you are tweaking the rig to get like 40 mph wide open! And what ever you try and adjust it all changes when you put another passenger onboard or extra gear like a cooler or a 60 lb trolling battery.

Just enjoy the boat as it is. Most boaters don't stay with the same boat that long anyway. You are going to want more HP's and a bigger boat someday anyway. I'm on my 5th boat over a 30 year period. So thats like a new boat every 6 years. Still want bigger. But I have to get a bigger tow vehicle first.

 

[catfighter]

Re: Boat motor seems to make a huge wake . . . Tohatsu 20hp

I also appreciate the help on this. I had no idea you have to "tune" the motor to the boat, though it makes perfect sense.

Now, if someone can help me catch flathead catfish during the spawn, that would be great (just kidding).

 

[Sea Rider]

Re: Boat motor seems to make a huge wake . . . Tohatsu 20hp

The issue about tuning motor height is because all hulls and transom heights are not same. Generally everybody just palces engine at back transom and out they go. Why is it a must have AC plate parallel to water surface at speed when boat is on plane. Just try this experiment. At 30 or more MPH take your hand out the window and place horizontal, will feel air flow passing with no effect, change wrist angle upwards, downwards what does you hand does, goes up or down, right.

If you already have a well ballanced perfect slinding boat on water surface why would you like to go out badly trimed and achieve excesive water drag on AC plate and up or down bow ride. Water has a much higher drag coeficient that air if we compare both examples. With a sharp knife try to cut in straright line a hard cheese while border is passing through at an angle that is not completely horizontal, where does the cut goes ?

 

[catfighter]

Re: Boat motor seems to make a huge wake . . . Tohatsu 20hp

One final youtube video of my boat at 3/4 throttle.

http://www.youtube.com/watch?v=oBeZjaA76VM&feature=youtu.be

Not sure how fast it's going but I'm going to estimate about 20 knots.

Let me know if the AV plate looks about right or if you think I should raise it another 1/4" or so (or if another 1/4" would make much of a difference) . . . .

 

[Sea Rider]

Re: Boat motor seems to make a huge wake . . . Tohatsu 20hp

That's the sweet perfect height spot congrats, have a tiny slight splash at right side of small upper plate, but assume it's due to having the videoman resting at near transom area and his weight changing slightly the engine/boat angle. If he sits up front at bow area, should dissapear completely. Or sit videoman at bow, you can come close to transom and visual check same as when filming while at wot.

The plate you are seeing out of water is not the antiventilation plate, is called small upper plate, water spray deflector. AV plate is way down water flow and doing what it's supposed to be doing, a good job indeed.

Happy Boating.

 

[catfighter]

Re: Boat motor seems to make a huge wake . . . Tohatsu 20hp

Thanks for the input. That splash is likely because I weigh 100lb more than the dude sitting port side. :facepalm:

This was fun, learning about tuning an outboard to the boat. I learned a lot!

 

[Sea Rider]

Re: Boat motor seems to make a huge wake . . . Tohatsu 20hp

Thanks for posting that fine video on Youtube, an excellent visual refference that will help match written tech data and assorted pictures to have a correct engine/transom height tuning.

Happy Boating

 

[catfighter]

Re: Boat motor seems to make a huge wake . . . Tohatsu 20hp

Another quick question!

Please check out this picture:

http://i68.photobucket.com/albums/i18/WoW_Zoth/4c288900.jpg


It seems as though the clamps are really close to the top of the transom now that I have jacked it up.


Is this safe?


Thanks for your help!

 

[BonairII]

Re: Boat motor seems to make a huge wake . . . Tohatsu 20hp

I would figure out a way to bolt the motor on. If you hit something while running, you could lose your motor.

 

[TOHATSU GURU]

Re: Boat motor seems to make a huge wake . . . Tohatsu 20hp

Yes, it is safe and you should run a bolt through the bolt hole in the engine clamp.

 

[catfighter]

Re: Boat motor seems to make a huge wake . . . Tohatsu 20hp

Yes, it is safe and you should run a bolt through the bolt hole in the engine clamp.

Thanks for the feedback.

There are two bolt holes on either side of the outboard but only one is below the aluminum strip. I'll run two bolts through them as soon as I figure out the best way to waterproof two holes in the transom. . . .


Also, this might be helpful to others who need to shim their motors:

I went to Lowe's and picked up a piece of 1" aluminum square tubing for $10. I cut two piece of it 10" long and taped them together. Now I have a 1-inch, strong, lightweight shim that will never rust!

And if you need a 1.5" shim, you can just buy the 3/4" square tubing and double it up.


The metal shop idea is a good one, but if you can't find one on the cheap you can try this route!

 

[BonairII]

Re: Boat motor seems to make a huge wake . . . Tohatsu 20hp

Thanks for the feedback.

I'll run two bolts through them as soon as I figure out the best way to waterproof two holes in the transom. . . .

3M 4200 works very well
3M 5200 is great, but permanent

 

[catfighter]

Re: Boat motor seems to make a huge wake . . . Tohatsu 20hp

So, I have read thread after thread about using caulk (4200 or 5200) to seal the bolts but no one actually explains how to do it.

how, exactly, do you seal the hole with caulk? Do you put caulk in the hole or do you put caulk on the bolt?


Probably a really stupid question but I would hate to get it wrong. . . . :facepalm:

 

[catfighter]

Re: Boat motor seems to make a huge wake . . . Tohatsu 20hp

Never mind; I figured it out. . . .

Thanks again, everyone, for the help!

 

[catfighter]

Re: Boat motor seems to make a huge wake . . . Tohatsu 20hp

So, for anyone interested how I went about adding transom tubes, here's how I did it:

1. measured the bolt size for my motor; they are 5/16"

2. cut a 1/2" pvc pipe to the width of the transom thickness. measured the outside diameter (5/8")

3. Marked placement of bolt holes on transom and drilled 5/8" holes. Inserted the PVC tubes (a perfect fit!).

4. used 5200 adhesive to permanently seal the tubes into the transom.

here's a picture:

http://p.twimg.com/AylxXHGCAAIR1mI.jpg


Hope this helps anyone reading this thread.

I know it's not pretty but neither is the rest of the boat!

 

[duke33]

Re: Boat motor seems to make a huge wake . . . Tohatsu 20hp

Glad you got it done bud! I learned on this thread myself.