Engine Height .. Please help!

[mikemac73]

Hi
I have 1985 Grumman 16ft aluminum boat. I have a 9.9 mercury. I am having a tuff time getting the boat on plane especially when by myself. I tried trimming and it didnt help to much. After reading some post about the height of the engine, it appears my engine is sitting a little to low. I measured where that fin on the motor or I think its called the cavetation plate should sit and it looks like it is about 3 inched to low. I bought a bracket to raise the motor on my transom. I attached a pic. Can someone please confirm that this is the right thing to do.

Thank you.

 

[tpenfield]

I would assume that the Merc 9.9 is the long shaft version. Transom is probably for a short shaft motor ???

Short shaft is for a 15" transom, long shaft is for a 20" transom.

 

[mikemac73]

my transom is 20 inches

 

[steelespike]

you need a longer piece from transom to the motor. you should lay it along by the keel out to the plate.
Plate is the plate above the prop.Is the boat a bare bones,no floor /bait tank etc.?
The pic does look like leg too long.

 

[flyingscott]

Part of the problem is that is a lot of boat for a 9.9 motor. Try putting more weight towards the bow of the boat especially if it planes easier with another person in it. I would also put a tach on the motor to find out the rpms because it could be struggling from being over propped for that boat.

 

[mikemac73]

Thanks Guys.
Yes I agree the 9.9 is not enough which is not helping at all. I am looking into getting a 30 or 40 hp . I bought at mini jacker to raise it up about 3 inches. I think it will help a little. I am fairly new to boating so this is all new to me. I appreciate the help.
Can you guys recommend a new outboard 30 or 40 hp ? I cant go more then 40hp.


thanks

 

[mikemac73]

steelsspike. it is a bare bone boat nothing in it but benches no floor.

 

[scout-j-m]

steelsspike. it is a bare bone boat nothing in it but benches no floor.

How wide and is it welded or riveted? I have a 1648 riveted Alumacraft which is listed as being 300 lbs. With a floor, TM, TM battery, fuel, and fishing gear it will get up on plane easily with two light adults with a Evinrude 9.9 hp 2 stroke. Does about 15 mph with two and 17-18 mph with just one. Prop is the factory 9 1/2 x 10" pitch prop. With a 15hp Johnson 2 stroke and 8" pitch prop it will do 18-19 mph with 2 adults and 20-21 with just one. Both motors run right at the top of their WOT range with a single person and a few hundred rpm less with 2 people so the motors are running well and are propped correctly.

 

[Sea Rider]

Mikemac,

Can you re post attached pic without showing wood strip placed on top cav plate, there are OB height/transom parameters to have in consideration.

Happy Boating

 

[jbcurt00]

IMO, unless glass flat still water, a 9.9hp is undersized for a 16ft boat, probably by at least half.

My 12ftr is rated for a 10 (or maybe even a 12hp) and the 14ftr is rated for an 18hp. I dont have any open fishong boat 16ftrs but, based on the other 2, a 9.9 is too small, even on an extremely light flat bottom jon boat.

Is yours a flat bottom jon or a semiVee?

As asked above how wide at the transom?

 

[mikemac73]

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[mikemac73]

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Thank you. The width is 51 inches on the transom. The center of the boat is almost 6ft wide. I attached some pictures.

 

[scout-j-m]

Mine is a true flat bottom jon boat with a short transom and shorter sides. Yours looks like it probably is heavier than mine. I would still imagine you could plane it with that motor though. Here is a picture of mine before I added any mods to it. Mine is rated for a 35 HP fwiw.

 

[Sea Rider]

Mikemac,

Some issues:

-That's a long shaft OB, and boat has a small V shapped bottom, at least at rear side, right ?

Alternatives :
-Is it possible to modify that 9.9 and pass it to a 15 HP OB ? that's if both shares same CC, a matter to check parts for both models differences, if so will increase hole shot power for combo to plane faster.

Ideal Leg Height :



-Ideal height is for water flow (2) at plane to skim right under(1) passing through sharp edge (5) OB must sit at 90? for boat and AV Plate to ride parallel to water level, deck weight must be evenly balanced.
-Would you say that portion (3) is even flat with (4), there's nothing in between that disturbs water flow when passing by?

-As combo doesn't plane as right now, don't know if need to raise or lower OB on transom to achieve that ideal cond, that's a bummer.
-If OB sits too low will experience water splashes out transom or even over transom.
-Need to know max achieved wot rpm, say you alone, or combined with a light boater sitting up front.
-Could install a induction tach to check that out, and then going for a prop maximization to pull out hole shot revs higher to plane faster.

Could go boating with a underpowered OB as long max passenger is max permitted to 2, along opt OB/Transom height seated, OB ridding at 90?, with deck weight well distributed with maximized prop (usually less prop pitch) if Merc has good prop selection availability for that HP model ? If still mission impossible to plane going for what's been suggested without passing actual OB to a 15 HP, will achieve a much better fast displacement speed than before.

Happy Boating

 

[Sea Rider]

Forgot to ask, what's current prop diam/pitch ? Would you say that when trying to plane combo, there's excessive water banging against back transom, is transducer splashing water also ?

Happy Boating

 

[jimmbo]

How about a picture that is shot level(parallel to the floor), not tilted up or down, and shot at the height of the bottom of the hull and another at the height of the anti ventilation plate. No wide angle focal length as that too distorts the image.

 

[Sea Rider]

Jimmbo,

Wil be useless, his problem is that combo doesn't plane at all due to underpowered OB. If would plane would be a different story as you could have water splashes out/over transom, areation issues which can be solved on water tests while moving up/down the mini jacker till the sweet OB height is achieved.

Raise fully the mini jacker and test again as previous runs, remove momentarily the transducer, could be adding aditional drag when trying to plane. OB/transom height testing should be dialed on flat calm no wind water cond and checking what's going on out transom.

Happy Boating