Boat run dry better with motor forward or back?

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Chrisco148
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Boat run dry better with motor forward or back?

Postby Chrisco148 » Tue Sep 10, 2019 7:23 pm

Hi everyone! Very excited about building my new rigging and am interested in your opinions on how far forward to mount my motor. Goal is to run dry!! Have a bit of back story to catch you up on why I’m on this question. I have a 472 direct drive caddy that started in a 16’ freedom craft, ran well but not a good boat on ground. Found a great deal on a 14’ floral city aluminum hull and rebuilt old rigging for the hull, quickly found this is not where I wanna be!!! In a hurry I locked a deal for a worn out 13.6’ cottonmouth with splash pan gone. Rebuilt rigging AGAIN but was concerned with the short sides so I pushed the motor forward where the prop was 13” from the transom, (pretty heavy motor and I carry 2 adults and two kids) all other hulls were setup by beer can standards on the transom. This hull ran amazing! Did everything I wanted to do! Ran dry anywhere, didn't porpoise in the river and didn't sit too low in deep water!!Unfortunately the bottom wore out and had to retire the ole girl, have been running the freedom craft since and hate it!! I just purchased another 13.6’ cottonmouth and am building all new rigging!!! So with that said here is where I’m at, I instantly want to build the new rigging as I built it before, 13” from transom and am happy to do so but I found that the low sides didn't really concern me in big water as much as I thought. This new hull has the splash pan still in it and feel that the motor positioned so the prop is in the pan may be better than cutting it out, but am wondering if the motor so far forward made the boat run better on dry? My goal is to run dry in the eagle, I do have to deal with deeper water in the river from the house but what runs better dry? Motor to the rear or motor farther forward?? I appreciate y'alls input and god bless!! :florida:
:old_glory: 13’ cottonmouth , 472DD, buddy Branch cam, 72" WW sig. series. :florida:

boatair
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Re: Boat run dry better with motor forward or back?

Postby boatair » Tue Sep 10, 2019 7:36 pm

Motor to the rear gets my vote.

Chrisco148
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Re: Boat run dry better with motor forward or back?

Postby Chrisco148 » Tue Sep 10, 2019 7:59 pm

boatair wrote:Motor to the rear gets my vote.

Any reason? What’s the thought??
:old_glory: 13’ cottonmouth , 472DD, buddy Branch cam, 72" WW sig. series. :florida:

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Deano
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Re: Boat run dry better with motor forward or back?

Postby Deano » Tue Sep 10, 2019 10:55 pm

Chrisco148 wrote: . . . but am wondering if the motor so far forward made the boat run better on dry?
Absolutely not.
That Branch DD Cam is to be credited for that.

Chrisco148 wrote: . . . but what runs better dry? Motor to the rear or motor farther forward??
Matters not. You are placing your concern on a comparatively irrelevant parameter.
The basic requirement is to have sufficient power to move the given amount of weight. Known around here as the Power to Weight Ratio.
Consider if you will, that forward/aft engine placement does nothing to alter either the HP available OR the weight to be moved.
Consequently, the Power to Weight Ratio is NOT changed; so The Song Remains the Same.
Your situation appears to exhibit the needed power for the weight at hand so you are good to go; unless you gain a LOT of weight.

The old adage of having the prop 'a beer can forward and a beer can down from the top of the transom' has stood the test of time because it works. There is little need or advantage to trying to fine tune the fore/aft placement of the engine beyond that, largely because there is no advantage to be gained by doing so.
If your engine, on your hull, makes it squat excessively in the water, that may
be a reason to move the engine forward, but it will not aid in its ability to run dry.

Now, the height of the crank/prop shaft(s) above the bottom, CAN make a difference in performance.
Generally, a lower center of gravity is perceived as being more conducive to a well handling, comfortable and safe boat.

Where the splash pan is concerned, I don't see the advantage.
It may have been a selling point back in the day, but how many do you see on new or even later model hulls?
Seems to me, that much weight (were it full) would continue to hold the transom down while it was trying to drain (a LONG time), whereas if the water were immediately in the bottom of the hull, it would not have additional leverage to lift the bow and sink the stern. I would rather be floating lower in the water with the bow where it is supposed to be, and not a foot higher. :shock:
Ultimately, it may not matter at all. Just don't let it give you a false sense of security.
Anybody can and/or will sink one at some point, with or without a motor well for their prop.
In that regard, all men truly were created equal. :D

Back to where we started . . .
Be aware that there is no difference in tuning a hull to run dry or run in the water. It is the same thing (in nearly all cases).
In other words, don't get hung up on "running dry". Sure that is your immediate concern, but it does not represent a different set of variables than does fine tuning a hull to be free running, even in deep water.
Reading and understanding what's in the following thread about hull tuning
will likely help you understand why your initial question nearly answers itself.
https://southernairboat.com/phpBB3/viewtopic.php?f=85&t=28600&p=276809
"The suppression of uncomfortable ideas may be common in religion and politics,
but it is not the path to knowledge; it has no place in the endeavor of science."
- Carl Sagan

Striker543
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Re: Boat run dry better with motor forward or back?

Postby Striker543 » Wed Sep 11, 2019 8:39 am

I think what probably made it push better on the cottonmouth with the removed splash pan is the fact that (I’m guessing) your engine was mounted much lower. Generally, the lower the push point (engine mount), the better the push. There is lots of information on here about that if you search.

Gangreen
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Re: Boat run dry better with motor forward or back?

Postby Gangreen » Wed Sep 11, 2019 1:21 pm

Back. Been there done that.

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Prototype
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Re: Boat run dry better with motor forward or back?

Postby Prototype » Wed Sep 11, 2019 11:59 pm

Why didn't you just rebuild your worn out hull instead of starting from scratch? Don't tell me these are 100 dollar budget fixes and running dry count's on friends pushing?
A fine boat is a month of tunning unless known parameters!

SWAMPHUNTER45
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Re: Boat run dry better with motor forward or back?

Postby SWAMPHUNTER45 » Thu Sep 12, 2019 9:07 pm

I don't think there is one answer to this question.

It is more a matter of the dynamic of a particular vessels shape and angle of attack than weight position.

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Re: Boat run dry better with motor forward or back?

Postby One Eyed Gator » Fri Sep 13, 2019 9:57 am

There are a lot of variables when you go switching hulls and riggings to start making apples to apples comparison.

My 2 cents would be motor as low as possible, prop back close transom (you used to see 3, 4, 5 and 6" prop adapters) to allow motor to be a little farther forward with prop still back by transom.

ole rule of thumb balance point should be 1/3 the hull length from the transom and motor level are really just a reference points I personally would not use a 6" adapter but I have it seen them run.

I ran a 472 Caddy setup in an 14' alumitec, 3/8' poly with SS rigging. I used a 3" prop adapter and the beer can rule was very low in the rear, maybe 6" of freeboard at an idle but it did run some dry. Like prototype said I spent at least a few months or better tweaking one thing at a time.

Getting a DD to run very well, takes attention to all the small details.

Good Luck


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