Engine Stand Advice Please...

  • Thread starter Thread starter GWTW-003
  • Start date Start date
Have you considered removing the splash-well?
Engine height is generally 48"-52" from the bottom of the boat to the centerline of the crankshaft. lower on a raceboat.
 
Since the air travels down the prop tips several inches before it starts blowing out you can get away with having it dip in the transom a bit if needed, have seen several fast boats dropping as low as stringer clearance will allow. Have also heard that going super low in a ride boat will cause alot of air swirl inside the hull, like blowing empty beer/soda cans out of baskets etc.
 
Center of prop flange to bottom of boat
http://www.southernairboat.com/phpBB3/viewtopic.php?f=48&t=25490&hilit=+prop+centerline
heres an old post but you may find some useful info in it.
 
Cut the splash pan out. I cut it out on an old cottonouth and dipped the tip of the prop in about 6-7" (cant remember off the top of my head). The boat handled wayyy better having the center of gravity lower. The previous engine stand had the prop dipped about 1" below the transom.

Also dont try and skimp by getting a shorter prop. Id get a different hull before a shorter prop lol. I ran an 82" on the aforementioned setup. Stick with the 80", chop out that splashpan, and let er eat!
 
when i build a motor stand i dont always use that rule of thumb .. i go by my prop bld from the transom u need to be consered with how low the prop sits below .. and 1.5" wow do not do that give more room for error ive dont a few stands built a few boat trust me thats not much. pitch your prop out max and give it 3-5" ive never had any problems with that is like the soda can rule .... soda can down soda can out also i wouldent run no less then a 78" prop on that 268 unless u go superwide u might get away with 76 but no less ....i had one of the last combee hulls made with out a splash guard they arent no good jmo.
your center line of motor would not change but u would loose 6-8" with that guard and being a smaller hull u need that room so maybe remove it ...
 
Don't be scared brother. Take a look in my photo gallery of my last boat when I was building the engine stand with a very similar setup to what you are doing.
 
The main part I like about the splash well is it keeps the crap in the bottom of the boat away from the prop, a few of my boats have had them, never got any water in any of them anyway so wouldnt hesitate cutting it out to gain a lower center of gravity. Do any of the glass hull manufacturers still use that design?
 
gyrocopter582 said:
Thanks for all the help guys.
Gonna have to give this some thought.
Click to expand...
well hell since i took off to build my own this week and havent got my damn hull i could always help ya out im n cocoa let me no :wink:
 
gyrocopter582 said:
I just measured again. If I removed the splashwell, and allowed 3" tip clearance,
from the stringers, I can lower the engine 7.5". This would place the tips 12"
below the top of the transom, and the prop centerline at 43" above the stringers.
Would this be acceptable? Would 'shrouding' the propeller this much 'cripple' it?
This ain't looking good, as I dam sure won't cut the transom down.
Click to expand...
u do not want it that low id go more topheavy on the motor side then my prop that low ... it will effect the thrust of the prop jmo u may wanna look into a bigger hull u dont have much to work with their ..or a hull that dont have that splash guard in it .look in my pics i have some that iv built the most ive ever ran a prop down was 8" and it was a 76" prop when i built the stand i had set it for a 72:

take all the advice u get in b4 u build it and ask why it runs like dookie ... look at the waterthunder boat he has 99% of his prop out the transom so his motors must sit a lil higher even being a ls the center line is based off the sbc
 
gyrocopter582 said:
I just measured again. If I removed the splashwell, and allowed 3" tip clearance,
from the stringers, I can lower the engine 7.5". This would place the tips 12"
below the top of the transom, and the prop centerline at 43" above the stringers.
Would this be acceptable? Would 'shrouding' the propeller this much 'cripple' it?
This ain't looking good, as I dam sure won't cut the transom down.
Click to expand...

I wouldn't go that deep lol. I wouldn't take the prop much deeper than 6" below the top of the transom.
 
you need to do the math of transome height minus stringer height half the prop length minus 6inches at the most that will give you six inches of prop in the boat that is the most i would set it up for
 
Photo044.jpg


Here ya go, 13'6" cottonmouth, 7' wide. 82" 3 blade R, 383 and a 2.38 stinger. I had the prop 7" into the transom with no negative side effects. I dont think you could go a lot further down than that, but I haven't tried. I don't remember how far the prop was in front of the transom.
Also if you look close you can see where I crudely chopped out the old splash pan lol.
 
gyrocopter582 said:
Had to go fix broken airplanes today, but I thought about the splashwell alot.
You guys are right (as usual), I'm gonna have to remove the splashwell.
SOO, now I have to decide how deep to sink the prop into the hull.
The splashwell is 6" deep, sighting across the flange, to the bow.
Comments show no deeper than 7" below the top of the transom.
Would 2" deeper, for a total of 9" below, really hurt it that much?
Click to expand...
what i can tell u from what i did with a 3 bld h 76" prop was take it 9 and seemed to lack a lil compared to the 72" 3bld h on push i had plenty of power so that dident hurt me it was to far in the hull ... jmo but ever on is different for 2" it aint really a big gamble just think it out ... good luck
 
7" is the furthest I have gone and the furthest I have personally seen. Maybe someone has done more? I can't tell you lol, but hey why not? LOL
 
Gyro,

Don't want to muddy the water, Yobee and James are giving you good advice. However, I will share an observation with you.

I don't understand how or why you arrived at thinking that you need to run an 80" prop on a 12' boat.
While it may be true that if everything else is equal, diameter will trump pitch, in this case it seems like everything else is not equal.

There are plenty of mild 350s getting by with much shorter props than that, especialy on a boat that small.
You can largely offset shorter diameter with more pitch if need be. As long as you have enough pitch to hold the motor back, why not go with shorter blades. A 76 or 78" Falcon prop (for instance) will more than contain a mild 350, and give you plenty of thrust to boot.

Additionally, the longer the blades are, the more torque roll you will end up with. On a small, narrow boat,
I would be inclined to deliberately run a shorter prop with more pitch to help minimize the torque roll.

Now if you already have an 80" prop that would explain why. Could you maybe get a shorter hub for it?

Not to imply for a second it ain't do-able, it certainaly is. Just pointing out that IMHO you don't really need an 80" prop for that hull.

Good luck with your build. :thumbleft:

Deano
 
gyrocopter582 said:
Had to go fix broken airplanes today, but I thought about the splashwell alot.
You guys are right (as usual), I'm gonna have to remove the splashwell.
SOO, now I have to decide how deep to sink the prop into the hull.
The splashwell is 6" deep, sighting across the flange, to the bow.
Comments show no deeper than 7" below the top of the transom.
Would 2" deeper, for a total of 9" below, really hurt it that much?
Click to expand...

I personally think it will work great that way! My prop goes 9"s below my transom and it will out run MOST of the Marsh boats out there. If 700hp did not blow my transom off when I was spraying N2o then there is not that much thrust coming off those last 9"s of blade since my fiberglass transom is built fairly light. But the prop will pull all of the water out of the boat for ya.

The best way I have had motor stand height explained to me is like this.

Place a half empty beer can on a hard flat surface and push with one finger from the top of can. (It will tip over)
Now Push from the bottom of the can..... and it will slide right along. 8)

Do you want your boat to constanly ride the nose and be sketchy? Or do you want it to ride free, fast and safe?

Being as your hull is only a 12x7 this is more important then ever. I personaly would only build that hull as a single drive front with single passenger rear, and make sure to move the seating back as far as possible!

It is also nice that you get the cage lower with the motor being lower as well.

I also think you would be fine with a 76" or 78" prop, a little less torque role with that small hull. I have 500hp with 78" and I wouldnt go any bigger. no thanks

Good luck.
 
I gotta admit I missed the 2.68 ratio in the beginning. :oops: My bad !

In spite of going back and re-reading that more than once, that small fact continued to elude me.

Still think you don't need that long a prop, but now I understand why you were in that mode.

Seems like a lot of folks want more gear. Heck, one already stepped up, sounds like it could be a win -win.

Good luck, Gyro. You'll be smilin' like a Cheshire Cat when you get there.

Deano
 
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