Prop height on deep v running twins

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Prop height on deep v running twins

Postby Michael » Thu Jan 11, 2018 8:41 pm

Hi guys altough my Crosby has twins it isnt a deep v hull so I have no reference point as to prop height for twins on a deep v hull. this is for an RC boat project I'm building
anyone have a definitive answer for me?
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Re: Prop height on deep v running twins

Postby Tom Brockmeyer » Thu Jan 11, 2018 10:40 pm

Michael,

The mini-Arneson surfacing drive can run 3/8" above the boat bottom because it's back so far... The water coming off the bottom "rises up" to the propeller behind the boat.  Your outboards will be much closer to the transom, so less water can "rise up" to the propeller in that case.  The longer setback allows the boat to plane off with the propshaft higher up.  Your outboards can not run that high without blowing out (slipping).

You'll have to tell us or show us how deep the keel runs in the water at full speed.  I believe deep V "real boats" with twins have the outer side of cavitation plate above the bottom and the inner edge below the bottom of the boat.  The leading edge of the cavitation plate would be dead even with the boat bottom.

Can you mount engines to a 1/8th inch thick aluminum plate to experiment with location?  The plate could have permanent mounting holes in boat transom and you could move the setback plates up/down and left/right while testing, then when you have it right, you could make a new mounting plate with only one set of holes OR mount the engines permanently in the desired location.

You can probably find lots of pictures to gauge from on google images...  (  fast v rc twin boat )
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Re: Prop height on deep v running twins

Postby creekrunner » Thu Jan 11, 2018 10:40 pm

........maybe something in this article will help.....section on V hulls........??
http://continuouswave.com/whaler/refere ... nting.html
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Re: Prop height on deep v running twins

Postby Michael » Thu Jan 11, 2018 11:56 pm

Tom
I can adjust height, I made an adjustable jackplate for the setback mount see video,  & due to the amount of setback the props of the outboards are just as far back as the inboard stinger drive shaft system and will be running in the same water situation which I why I think I should replicate the setup that exists on the inboard boat and get the outboard props at  the same height

the boat is out of the water and runs on the back 2" of the hull see video in slowmo

thanks buzz will read that material
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Re: Prop height on deep v running twins

Postby Michael » Fri Jan 12, 2018 12:31 am

others seem to see this as I am
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Re: Prop height on deep v running twins

Postby outboard315 » Fri Jan 12, 2018 3:01 am

There is a picture of a vintage offshore race boat with 4 125bp on the back, the center two were long shaft and the outer two are short shaft and they all are level across the top. I thought the rule of thumb was the prop shaft level with the bottom and use the jack plate to go up or down from there.
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Re: Prop height on deep v running twins

Postby zul8tr » Fri Jan 12, 2018 2:32 pm

Michael wrote:Tom
I can adjust height, I made an adjustable jackplate for the setback mount see video,  & due to the amount of setback the props of the outboards are just as far back as the inboard stinger drive shaft system and will be running in the same water situation which I why I think I should replicate the setup that exists on the inboard boat and get the outboard props at  the same height

the boat is out of the water and runs on the back 2" of the hull see video in slowmo

thanks buzz will read that material
phpBB [video]


The prop height with the single screw is at the center of the hull and with the 2 outboards obviously off center the relative prop height from the Vee bottom will be different. You state that the outboard props are set back the same as the single screw setup, however the water feed to the outboards will not be the same as the single screw. It looks like the outboard hull has no lifting strakes or will you be adding some  :?: Therefore the water will rise up the Vee without strakes (different than with them) and will approach the offset outboards differently than it does to the the single screw. Also if both your outboards have props turning in the same direction water feed to the props would be different for each outboard (do they make counter rotating RC set ups  :?: ) As a start I would shoot for setting the outboards relative to the sloping Vee lower than you have for the single screw height relative to the hull center. How much lower  :?: My guess put the prop shaft center even with the Vee hull at the center of the outboard locations if not to far apart. As for spacing at a minimum I would try 4 prop diameters apart measured from the prop shaft centers and adjust height as needed at the Vee bottom. Will the engines still fit and turn with this dimension or is wider needed :?: As with full size and models testing is the real answer, prepare for mods.
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Re: Prop height on deep v running twins

Postby Michael » Fri Jan 12, 2018 5:04 pm

thanks guys Im going to mount them with prop shafts even with the bottom of the V and I will be using counter rotating props or I fear it will lay over on its side and stick there if the throttle gets hammered
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Re: Prop height on deep v running twins

Postby Tom Brockmeyer » Fri Jan 12, 2018 5:20 pm

Michael,
Is the plan to move the battery forward or to put ballast in the front of the new boat to counter twins hanging off the back..?
Tom
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Re: Prop height on deep v running twins

Postby Michael » Fri Jan 12, 2018 5:37 pm

Tom Brockmeyer wrote:Michael,
Is the plan to move the battery forward or to put ballast in the front of the new boat to counter twins hanging off the back..?
Tom


yes Tom there is a ton of room for 2   3S 5000 Mah 12volt batteries, the weight of one battery will counter balance the weight on the transom

I found a guy that did this but just as he was getting it dialed in he snapped a prop shaft and none were in stock for a year the only issue he had was the boat would lay on it side and stick there if he nailed the throttle too hard and that was due to both props turning the same direction.....and as stated I will run counter rotating props,  

let the drilling and cutting begin :twisted: this part makes me nervous every time, I have as much $ in these remote control boats as many of us do in real size boats

this is how it sits in the water with the 2 heavy 3S 5000mah batts with the inboard setup I wired them in series to make 6S 24volts & 78mph is the fastest time to date

WP_20170910_12_36_18_Pro.jpg
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Re: Prop height on deep v running twins

Postby creekrunner » Sat Jan 13, 2018 1:56 am

....I've read that these flex prop shafts have  a short life span. When bought my motor ( same as yours), I also bought a spare. Since then, I ordered 3 more while still in stock. You mentioned earlier using marine grease thinned a bit with a light oil. What do you use to inject the lube ?
Experience is a wonderful thing...........it enables you to recognize a mistake when you make it again.....
Buzz Lindberg...Make 'em run 1st, then deal with the  "pretty factor"....or not..
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Re: Prop height on deep v running twins

Postby Michael » Sat Jan 13, 2018 2:22 am

Ive since switched to blue marine grease and this gun it creates enough pressure to get that thick stuff into every crevice
that thick marine grease does slow me down a bit but I stopped snapping flex shafts  :mrgreen:
https://www.amazon.com/Astro-101-Grease ... B000FMK7FG

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Re: Prop height on deep v running twins

Postby creekrunner » Sat Jan 13, 2018 3:14 am

thanks...... icon_thumbup.gif  icon_thumbup.gif
Experience is a wonderful thing...........it enables you to recognize a mistake when you make it again.....
Buzz Lindberg...Make 'em run 1st, then deal with the  "pretty factor"....or not..
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