Height of 9.9 tohatsu

[flangler]

I was reading another thread and it was talking about the height of your upper plate on the motor. And that the water should be passing just beneath it to prevent drag. However I was running my boat and noticed that my upper plate is below the waterline. Should it be just above the water line? I would have to raise the motor substantially to obtain this. Doing so would I need a jack plate? What size shaft is considered a long shaft? Any answers would be appreciated! Thanks!

 

[JB]

Re: Height of 9.9 tohatsu

Hi, flangler.

Shaft length is measured from the transom clamp surface that sits on top of the transom to the anti-ventilation plate. Short shafts are nominally 15", long shafts 20". Correct rigging starts the anti-ventilation plate level with the bottom of the transom/. Fine tuning may raise it another inch or so.

If you have a short transom (15" +/-) and a long shaft outboard (20" +/-) a jack plate is a good solution.

 

[flangler]

Re: Height of 9.9 tohatsu

Thank you very much! I'm going to take a look at that. If it is a long shaft and is running to low, will that effect the performance of the motor/boat? And how?

 

[TOHATSU GURU]

Re: Height of 9.9 tohatsu

Yes, it will. It will be slower, throw water into the boat and keep you from running in shallow water.

 

[flangler]

Re: Height of 9.9 tohatsu

Gaining some speed is definitely a plus. However, I don't get water in the boat. I'm going to address the situation for sure!

 

[Sea Rider]

Re: Height of 9.9 tohatsu

Ideal setting would be ; with engine properly trimmed and boat well ballanced, at wot, water flow must pass slight under small plate and parallel to water surface.

Happy Boating

 

[flangler]

Re: Height of 9.9 tohatsu

Agreed. Today I measure the shaft and it was 17" give or take and the transom is 16". So it's about a inch to low. Now would it make a noticeable difference to raise it? There isn't that much room left on the transom, and I would have to drill and plug existing holes. Is it worth it?

 

[Sea Rider]

Re: Height of 9.9 tohatsu

If you don't have excesive water splash at boat's side or water intrussion over the engine inside boat could leave as it is, test at wot and check to determine how much you will need to raise the engine for best top speed and performance. 1" is too small for a jack plate, generally are for 5" transom rise, but could place wooden shim on top transom to raise the engine a bit. Not all engine brands performs same, each has their own parameters to watch for. As said before Tohatsu's are natural water splashers compared to Yams if not seated correcty on transom, a lower tail design issue.

Happy Boating

 

[JB]

Re: Height of 9.9 tohatsu

I don't agree. Putting the AV plate below the water when on plane is going to create excessive drag.

Put the engine on the transom, Flangler. Then measure how much the AV plate is below the transom bottom with the prop shaft horizontal. I think you will find more than 1", due to tilt in the transom.

 

[Sea Rider]

Re: Height of 9.9 tohatsu

JB, assume we are confusing terminology. AV plate is the larger & wider horizontal plate located at lower tail, right. I'm reffering to the small upper plate, should be slight above water line. Being just a 9.8 HP eventually will have some water splash at back transom because of tail design and transom height if engine it's not correctly seated, a Tohatsu issue.

To check on spot, place a mate at bow as a counterweight for horizontal cruising, go wot, once on plane driver should look behind the engine to see exactly what is happenging at rear transom. If water flow is passing slight under small plate will be passing through the triangle tail area cutting nicely water flow, if passing above upper small plate will be passing through the non triangle area, an area that produces non water flow cut, but does produce side or internal splashes that are a bummer reducing top end speed and neat engine/boat combo performance.

These tips were severely tested under trial & error as most of the time what is written in owners manual is just a refference from where to start.

Happy Boating

 

[flangler]

Re: Height of 9.9 tohatsu

I'm going to take a look at it. I will get back to you guys and let you know how it goes. I have a good idea of what to do!

 

[flangler]

Re: Height of 9.9 tohatsu

So here's a pic I forgot I had taken today. As you can see the anti-ventilation plate is lower the the hull, but the upper plate is pretty high. Maybe because it's a tiller motor and there's more weight in the back of the boat it sits lower. Is does look a lot like the other picture in the thread. What do you think? Maybe move some weight to the front to offset my weight?

 

[TOHATSU GURU]

Re: Height of 9.9 tohatsu

Your engine is mounted too low. Raise it up in 1/2 increments until you find the best spot.

 

[Sea Rider]

Re: Height of 9.9 tohatsu

Frangler, what is your actual transom/hull height in cm to start with ? A pic won't tell you a thing, cruise perfection is done under trial & error. Don't be lazy test for yourself, we've been doing so with all Tohatsu engines up to 50 HP for the last 3 years. Used to have Evi & Yam 15 and both behaved entirely different to Tohatsu, different lower tail design.

To get the idea straigh : Place your trim at 2/3 hole out transom, start with (2) place a mate upfront bow, must not be a sumo fighter, could be same weight as yourself, this is to achieve a parallel boat on sea surface and engine at 90?, full wot, once on plane, check rear tail and see where is water flow passing by, there's not a big issue with small side splashes, could place 2 side splashguards, but if water in entering boat by middle transom must raise engine accordingly as water flow is hitting the non triangular area previously described.

Will end saying ; if you use Tohatsu S engines will need 40.0/40.5 cm transoms heights in order for engine/boat combo to perform as expected. These tips could be applied to any type of boat, but will leave this to sib/ribs for the moment...

Happy Boating

 

[flangler]

Re: Height of 9.9 tohatsu

My transom is 40.6 cm, so it should be a good fit. As far as 2/3 hole you mean the setting that places the motor at 90 degrees to bottom of boat. Don't mind my ignorance, I'm learning. As far as water testing that won't be a problem. As stated above, should I start with 1/2 in. increments?

 

[TOHATSU GURU]

Re: Height of 9.9 tohatsu

"As stated above, should I start with 1/2 in. increments? "

Seriously?

 

[flangler]

Re: Height of 9.9 tohatsu

Just asking a question.

 

[TOHATSU GURU]

Re: Height of 9.9 tohatsu

Yes, you were....

 

[Sea Rider]

Re: Height of 9.9 tohatsu

Flangler,

Is the pic you have posted correspond to the combo you are requesting information about ? Asume you have not tested that boat on water yet, right ? Theoretically that engine will be well seated with 40.6 cm transom to lower keel, why would you need to rise it more, you won't know until you go for boat/engine water test at wot. Which is the max HP rated for that boat ?

Near Happy Boating

 

[TOHATSU GURU]

Re: Height of 9.9 tohatsu

Omg