CG for my Dumas SK Daddle 36"??

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dannyual767

Well-Known Member
Joined
May 27, 2004
Messages
633
I'm about to drill holes in my stringers to mount the engine. When I built the hull, I moved the stringers out to the standard 5" spacing so I could use popular vibration absorbing motor mounts. I've got Aeromarine 5" mounts for both my OPS 11cc engines and now for my new K&B 11cc as well. I'd like to be able to switch between engines if I want.

Anyway, any ideas? I know that it may not have been too critical with the underpowered engines of the day in the 60's and early 70's, but I think that I better get this pretty close or my boat will blow over easily. Thanks.
 
dannyual767 said:
I'm about to drill holes in my stringers to mount the engine.  When I built the hull, I moved the stringers out to the standard 5" spacing so I could use popular vibration absorbing motor mounts.  I've got Aeromarine 5" mounts for both my OPS 11cc engines and now for my new K&B 11cc as well.  I'd like to be able to switch between engines if I want.
Anyway, any ideas?  I know that it may not have been too critical with the underpowered engines of the day in the 60's and early 70's, but I think that I better get this pretty close or my boat will blow over easily.  Thanks.

69474[/snapback]

Being familiar with these hulls i can say put the center of the motor 16 to 16 1/2 inches from the transom. the most important thing about these hulls is to use trim tabs and have a little 'rocker' in the hull (roughly 1/16 inch upward curve in the bottom of the hull in the last 4 to 6 inches measured forward from the transom) this allows the hulls attitude to be adjusted (preferred setting for me is right on the edge of disaster)

here's a pic of a recently built SK-daddle and the scratch built runnerbottom drag boats I've been building.

good luck

Steve
OLDSCHOOL.jpg
 
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Flyin Rat, those are really nice looking boats! How long are they? Do you have any other pictures with full installations?

I measured how far I've got my engine sitting right now and it's just under 16" from the transom. To go any further, I'll have to cut a hole in the bulkhead for the carb. If you really think that I need to get the weight further forward, I'll cut the bulkhead. Remember, my boat is only 36" long.

I just want the boat to have the best chance to run right. I've got a lot of power with these 11cc engines and I know that this hull was never designed for this much power so I'd better have the setup pretty close to perfect or I'll never be able to give it much throttle.
 
dannyual767 said:
Flyin Rat, those are really nice looking boats!  How long are they?  Do you have any other pictures with full installations?
I measured how far I've got my engine sitting right now and it's just under 16" from the transom.  To go any further, I'll have to cut a hole in the bulkhead for the carb.  If you really think that I need to get the weight further forward, I'll cut the bulkhead.  Remember, my boat is only 36" long. 

I just want the boat to have the best chance to run right.  I've got a lot of power with these 11cc engines and I know that this hull was never designed for this much  power so I'd better have the setup pretty close to perfect or I'll never be able to give it much throttle.

69577[/snapback]

I wouldn't start cutting ,just get it as far forward as you can. hull shape and trim tab settings are more important than CG. remember these are meant to go straight and fast and with the tabs and about only 1 or two inches of the boat wet at speed.remember the full sized ones have the blown 454 on the back 25% of the hull.

my hulls are 43 in long and am building one with an O.S. Max 81.... pics to follow

Steve
 
Yeah, I really didn't want to go cutting that bulkhead if I didn't need to. I'll just mount the engine as far forward as possible with adequate carb clearance.
 
I note that FRS is using a surface drive with the prop positioned well aft of the transom; I assume it is a steerable outdrive(?). This is a very good idea for maximum straightaway performance on a flat-bottomed boat. With the prop well back it increases the "wheelbase" between the last few inches of the hull and the prop to help stabilize the boat in pitch. The surface drive lets the motor turn up and the prop to unload; both features should increase the performance of the hull significantly. Like any model it will still have a "maximum speed" limit, but this modification should raise that. I'd love to see videos of either SK boat. B)
 
Of course I won't have a cool looking outdrive like FRS has but my prop will still be way behind the transom. I've got Speedmaster style hardware. Front edge of the prop will be about 3 1/2" from the transom. I've got another strut with a skeg that will put the prop about 2 1/4" from the transom unless I use longer brackets.
 
actually the outdrive is not steerable (just dont have the rudder mounted in pics) the outdrive is homemade (with minimal tools)

normal_outdrive.jpg
 
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