planing help

Boat-ryder

Petty Officer 3rd Class
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May 19, 2012
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87
I need some help guys.

i got a 16' lowe semi tunnel hull jon that i cant get to plane out.when i first got the boat it had a 25hp johnson that i got to plane once only because i hit another boaters wake. now i have a 35hp evinrude but still cannot plane.i was having alot of problems with boat drag because the motor sat to low mainly because of the tunnel.i bought a manual jack plate and got the cavitation plate about a half inch from being level with bottom and it now has a 4in offset but it still isnt enough.any ideas? i havent played with my tilt very much not sure which way does what. do you think i just dont have enough motor for the boat?any help greatly appreciated
 

Mi duckdown

Commander
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Apr 14, 2007
Messages
2,575
Re: planing help

Probably need to raise motor. Got Pics of setup? tunnels are a different animal. Have contacted Lowe for help?
 

Boat-ryder

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May 19, 2012
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87
Re: planing help

i can take a pic tonight.no havent talked to lowe but would a half an inch make that much difference?before the water out of tunnel was hitting foot and spraying everywhere.now that i got the jack plate the water is hitting just under the ribs above the cavitation plate and getting a little spray.the one and only time i know it was really planing, water was only going backwards no spray
 

Mi duckdown

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Apr 14, 2007
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2,575
Re: planing help

Water is hitting above the vent plate. Not good. Where are your pics?
Boat- ryder I don't want to be a Smart ***** but the set up on those boats need to to run off the water comming off the water from the transom in clean water. PICS PICS. I'm Done without PICS
 

jestor68

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Jun 12, 2012
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2,308
Re: planing help

When you say the boat won't plane off, what exactly is it doing? Is the prop ventilating and the motor reving, but not able to push it up onto plane?

Those Lowe "tunnel" boats are referred to as "tunnel jets" by Lowe. I do believe they are intended to be powered by outboard jet drives for running in shallow water.
 

UncleWillie

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Oct 18, 2011
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3,995
Re: Planing Help

Re: Planing Help

While I am no expert on OBs by any mean....

I might suggest that you Trim IN all the way to start.
Trim In = Bow Down; Out = Bow up!
And/Or get some weight (Passenger?) into the bow to flatten the ride.

The Anti-Ventilation (AV) Plate should be wet on the bottom and dry on the top when on plane.
Just skimming the surface.
Hold a long straight edge against the tunnel to see where it lands on the AV Plate.
Start with the AV Plate an inch or two above the plane of the tunnel.

If the prop Ventilates (Sucks Air), Lower the motor an inch.
If it doesn't, keep raising the motor until it does, and then lower it back to where it didn't.

TunnelTrim.jpg
 

Boat-ryder

Petty Officer 3rd Class
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May 19, 2012
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87
Re: planing help

ok my motor must still not be high enough because the water is hitting off of the ribs right above the cav plate so both sides of cav plate are wet.and i will try trimming it in all the way.my bow is coming up but not too much, im just not skimming the water
 

Mi duckdown

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Apr 14, 2007
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2,575
Re: planing help

In My opinion, you are still to low. The only way to figure this IS to unclamp motor from bracket and place 2" square tubing under clamp and retighten. Water test. If to high go to 1 1/2" 1" untill you find the sweet spot. Looks like you have a long shaft motor on there. YES?
 

UncleWillie

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Oct 18, 2011
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Re: planing help

In My opinion, you are still to low... Looks like you have a long shaft motor on there. YES?

Looks too long to me too. ;)

What is your transom Height? and Shaft length?
The transom height is the distance from the tunnel to the transom edge.

The shaft length is the distance from the bottom of the mounting clamp to the bottom of the AV Plate.
The shaft length is hard to measure directly, but it will be a multiple of 5.
So if it looks to be something like 21-1/2, it is a 20.

TransomHeight1.jpg


-----------------------------------------
P.S. It is an Anti-Ventilation (AV) Plate not a Cavitation plate.
Ventilation and Cavitation are two completely non-related phenomenon.
Sorry to be the language Cop. :D
 

Boat-ryder

Petty Officer 3rd Class
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May 19, 2012
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87
Re: planing help

i will measure soon as i get home tonight.i dont think its a long shaft. from what ive seen other long shafts look like.thinking about what your saying about the spacer i dont think i can go 2 in without my clamps being right on the top edge of jack plate which i wouldnt trust but i can raise plate up a hole and get about an inch and then add a 1 in spacer and still keeps the clamps in a safe spot.will let you know soon.thanks
 

Mi duckdown

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Apr 14, 2007
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Re: planing help

Boat- ryder. I quess I wasn't completly clear. My Bad. my post was just to give an idea of how high to raise it for a temporary fix. When that issuse is solved, then you can mount the motor permanently at what ever height is needed.
 

Boat-ryder

Petty Officer 3rd Class
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May 19, 2012
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87
Re: planing help

Ok I got ya, just measured, my shaft is 16 in and transom from top to top of tunnel is 14 1/4. If I didn't have the tunnel the av plate would prolly been in the perfect spot. Just for my knowledge 16 in is short shaft right? Looks like rain this weekend but will update soon as I can water test. Thanks for all the help
 

smokeonthewater

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Dec 3, 2009
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9,838
Re: planing help

"bottom of the mounting clamp"

the highest point inside the clamps that the top of the transom could possibly be.

typically, 15" = short, 20" = long, 25" = extra long.... of course there ARE both longer and shorter motors than those.
 

Mi duckdown

Commander
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Apr 14, 2007
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2,575
Re: planing help

Actually 15" is a short shaft. Are you measuring from the bottom of the clamp that sits on the transom too the AV plate, just above the prop?
Buy a raincoat.
 

Boat-ryder

Petty Officer 3rd Class
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May 19, 2012
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87
Re: planing help

yes just as the picture "unclewillie" posted it measured 16 in
 

UncleWillie

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Oct 18, 2011
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3,995
Re: planing help

yes just as the picture "UncleWillie" posted it measured 16 in

That would make it a Short(15) Shaft Motor.
The engine is trimmed out a hole and the clamp is at an angle, and you likely are not measuring Exactly Parallel to the shaft but at an angle.
This is a difficult measurement and all the little variables tend to make the number a little bigger. 16 = ~15 = Short.

If the transom is 14-1/4 = ~15 you are a close match.
If the jack plate raises you 4 inches you should be good or possibly a little high.
The other factor is the jack-plate and the Tilt combine to position the drive well behind the transom.

While running at speed, as the water exits the tunnel it will tend to raise up to fill the hole left by the boats displacement.
This raises the water line a bit. Think of it as a mini Rooster tail.
That should be OK as the drive IS up a few inches to match.

I would like to see another picture taken from about 5 feet Directly aft of the prop, looking up the tunnel.
Position the camera EXACTLY at the level of the top of the tunnel.
This will show us the relationship of the Vent Plate to the tunnel.

A side view with someone holding a long straight edged object pressed against the tunnel and extending past the drive would help also.

Having water on both side of the Vent plate is not an issue at this point.
You are NOT on Plane, and a submerged vent plate is to be expected.

It is time for another Sea Trial, Trimmed down all the way, and a passenger in the bow.
We need to get it on plane before we can do the minor tweaking stuff!
 

smokeonthewater

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Re: planing help

Try this: pull the tilt pin out and trim the engine ALL the way down.... measure again..... I know pics can be deceiving but it still looks long to me... I think that MAYBE being trimmed out is throwing off your measurement.
 
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