Boat will not get up on plane and is really slow???

Automotive powered airboat discussion.
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Deano
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Re: Boat will not get up on plane and is really slow???

Postby Deano » Sun May 21, 2017 10:39 pm

That is good news then. Based on that, you're issue would surely
seem to be either engine angle or prop pitch or a combination of both.

Sounds like a boat ride w/ a few tools should solve your problem.
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Re: Boat will not get up on plane and is really slow???

Postby Runnin_gunnin24 » Sun May 21, 2017 10:43 pm

Deano, thanks for the help will be back on the water soon with tools in hand hopefully it will just take a little tweaking and I'll update when I get it figured out.

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Re: Boat will not get up on plane and is really slow???

Postby Warden » Sun May 21, 2017 10:49 pm

How bout on dry ground ? If u take the plowing water out of the equasion ? I would
Think the angle would matter less with a solid bottom ? I dont know about props ... i know about engines , i assume if the pitch is enough to produce thrust then the prop is what holds the engine from
Banging past 3000 ? I do an awful lot of travelin each month for "perfect running engines "'
And the issue is clamed to be elsewhere .. only to find sour engines or assembled wrong !
If this cant happen on an airboat then disreguard please ... but wow does it happen with race cars and tractors and boats ! That being said ... 3000 rpm is 3000 rpm ... if the load is the same
Then the drop from 37 to 5 seems less then possible 2 me ! But im stupid and i can prove it

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Re: Boat will not get up on plane and is really slow???

Postby SWAMPHUNTER45 » Mon May 22, 2017 7:07 am

It is really hard to grasp how an exact replacement build, turning the same blades, pitched at the same mark at 3000 rpm and using the exact same mounts / rigging could be acting this way. Maybe consider putting a level on the rigging at the base and adjust the trailer attitude to level. Then take a reading off a valve cover and see what you get.

As suggested try dry ground or if your trailer allows you to safely power test, hook it to a vehicle and see if it will push a truck around. Again you need a trailer designed and capable to perform this test and ensure it is properly secured.

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Scotty1
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Re: Boat will not get up on plane and is really slow???

Postby Scotty1 » Mon May 22, 2017 8:11 am

:rebel: ARE your leading edges turned inward towards the motor or towards the back . cant really tell from the pictures but they should be angled towards the motor ,you could have angled the wrong way or blades switched from side to side it almost looks like the blades leading edge is angled to the rear :rebel:

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Re: Boat will not get up on plane and is really slow???

Postby Scotty1 » Mon May 22, 2017 8:20 am

:rebel: after clicking on the pictures that not seem to be the case, the washer deal sounds like the fix :rebel:

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Re: Boat will not get up on plane and is really slow???

Postby Scotty1 » Fri May 26, 2017 6:58 am

:rebel: Did you ever get it worked out :rebel:

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JAMES
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Re: Boat will not get up on plane and is really slow???

Postby JAMES » Sun Jun 11, 2017 10:12 pm

Carb the same ! Many issues i could think of .. carb, compression, timing, distributor module ect ect all that could play factor
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Re: Boat will not get up on plane and is really slow???

Postby Kpeterson » Wed Jun 28, 2017 2:50 pm

Check your timing and that you're not off a tooth on the timing gear. I did the same thing built a new 350 with cam etc same prop and gearbox and wouldn't go above 3200 RPM. Didn't figure out that I had the timing gear off a tooth until I blew the motor up test riding it.


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Re: Boat will not get up on plane and is really slow???

Postby Runnin_gunnin24 » Thu Aug 03, 2017 7:39 pm

Hey guys for the delay between post but been really busy with work. I tried the washer thing and didn't work I did find that the adjustment on the prop was off one was at 10degrees and the other at 12.5 I set both at 10degrees and it's running a little bet I but not like it was before I'm running 20mph now but if I turn the boat or go from shallow water to deep it doesn't stay on plane I'm at a complete loss and with me being in Illinois there are no local shops or people to talk to thanks in advance for any further advice

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Re: Boat will not get up on plane and is really slow???

Postby GeeLeDouche » Wed Sep 13, 2017 4:11 pm

add more pitch. see what it does.
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Re: Boat will not get up on plane and is really slow???

Postby sanshandaobojue » Thu Sep 14, 2017 6:30 pm

Runnin_gunnin24 wrote:Hey guys for the delay between post but been really busy with work. I tried the washer thing and didn't work I did find that the adjustment on the prop was off one was at 10degrees and the other at 12.5 I set both at 10degrees and it's running a little bet I but not like it was before I'm running 20mph now but if I turn the boat or go from shallow water to deep it doesn't stay on plane I'm at a complete loss and with me being in Illinois there are no local shops or people to talk to thanks in advance for any further advice

if the propeller at same pitch , and running at same direction and speed 3000rpm as before, it should same thrust force as before. I guess the speed on mechnical tach is wrong, try to get a digital tach to measure the flywheel or propeller directly. If the pitch is right and speed is much lower than before like 2000rpm , u will get this cituation, without much push , little thrust force.

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Re: Boat will not get up on plane and is really slow???

Postby Runnin_gunnin24 » Sat Sep 30, 2017 10:20 pm

Hey guys I checked the timing and found it was off. Now boat has a lot more hp and it's finally getting across the water. I do have an issue with the boat being slower since the rebuild. I was running around 37mph and now my top speed is 25 and it seems that the front end is still digging a little. Should I try the washer route again now that I know I have the hp to get the boat up on plane? Any advice would be great thanks.

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Re: Boat will not get up on plane and is really slow???

Postby kwanjangnihm » Sun Oct 01, 2017 5:55 am

Runnin_gunnin24 wrote: was running around 37mph and now my top speed is 25

this is still a big difference - it still sounds like your timing is not correct :scratch:
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Re: Boat will not get up on plane and is really slow???

Postby SWAMPHUNTER45 » Mon Oct 02, 2017 8:01 am

There has to be a mechanical difference in your rebuilt engine or several issues coming together in concert to have this effect. Generally these causations would lead to a substantial power decrease.

Things to cross off the list:

Camshaft not degreed, damaged or different spec not well suited for DD
Compression decrease or possible dead cylinder
Decrease in overall displacement especially the stroke in DD (350 vs 383 or 400)
Carburetor not functioning properly

As it relates to ride quality if everything is identical it would be extremely odd to see a change in the boats ride. Did you change the bushings or use a different engine mounting component? I can tell you that in conical mounts going from an older soft (blue) and compressed bushing to a new harder compound like the (white) hard poly bushing can make a sizable (in excess of 1/4 inch) change in your engines mounting angle. If you in error had two different compounds and swapped them around that would be a possibility.

Where are you located?

If your sure your power is identical then work on tuning the engine angle bringing the rear up and/or front down.


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