Newb needs help on vintage Dumas Hydroplane

[dpetsel]

I am a CAD scratch designer/builder of large scale Electric RC planes. Someone from our club brought in a box of old rc stuff and in the box was a damaged Dumas Atlas Van Lines #1304. Since I love to build I thought I'd take it on. (I always wanted one of these when I was in high school back in the 70's) I had to resheet 1 sponson, repair main deck and make a tip for 2nd sponson. I have done all the repairs and am now fitting parts. I had a nice 36mm EDF motor out of a large Starmax F4 that had crashed. It is a 2000 watt, 1500kv roughly 2.5 HP on 6s. Looks a lot like a Neu. It was a screamer in my jet. The original owner of the boat had a 7.5cc K&B engine in it with a solid 2 part 3/16 shaft with Octura joints and a Z60, 60mm Octura plastic prop. I have removed the solid shaft and have a 3/16 Octura flex shaft on the way. I have a Leopard 5698 but any 56mm motor would be too heavy and too large for the hull. With my 36mm and a 4000mah 6s bat and all electronics I get a good CG about 1.5" from back of sponsons. Since this is my first boat I am not interested in max speed right now but am wanting it to at least get up on plane. I realize that by todays standards it is a real heavy boat. By all comparisons I am putting out more power and RPM's than the stock K&B engine. Is my thinking cogent? Any info would be great.
Thanks,
Dave in Iowa

[Fluid]

Beautiful build! Wish I had the skills.

A 36" hydro is typically powered by 6S, but almost never by a 36mm motor with such a high Kv. That motor lacks the torque needed to spin a large prop and amp draw will likely be excessive. Plus it may not plane the boat. A 40mm X 82 mm motor is called for, with a Kv closer to 1200; even a Kv of 1000 would work well for a heavy sport boat.

Suggestion:

http://www.offshoreelectrics.com/pro...?prod=leo-4082 Choose the 1000 or 1250 Kv.

And this ESC:

http://www.offshoreelectrics.com/pro...seaking-180-v3

And no plastic prop! An x447 or x450 should do well safely. These choices will work far better than what you have. Using what you have risks poor performance and a melt down.



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[Tails Up]

Nice restoration! COG (center of gravity) should be at 1/3 overall hull length from the transom. I am new to electrics,so I can't offer any help there. Posts some vids of it when you get it going,its a cool boat.

[JimClark]

I think the CG will be more like 1 to 2 inches behind the back of the sponson's. 1/3 of the length from the transom will be way off

Nice restoration! COG (center of gravity) should be at 1/3 overall hull length from the transom. I am new to electrics,so I can't offer any help there. Posts some vids of it when you get it going,its a cool boat.

[dpetsel]

I think the CG will be more like 1 to 2 inches behind the back of the sponson's. 1/3 of the length from the transom will be way off

Thank you Jim.
I had read that and my current CG with all electronics is about 1.5" behind sponsons.

I have read just about everything I can on these hydro conversions.
I read a bunch of your posts back in 2003,2005 etc., with Andy Kunz (now with Spektrum) about your electric power plants for these hydros. I thought my setup is more powerful than the original KB gas and Andy was running Astro 25/5's in a similar boat. You think I can at least putt around on plane with my current set up?
Thanks
Dave in Iowa

[Fluid]

Setting the CG 1/3rd ahead of the transom is appropriate for a mono, NOT a heavy sport hydro. It will drag the transom, pull a lot of amps and probably will not even plane. Jim is right, closer to 2" behind the sponsons is right.


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[JimClark]

How heavy is that boat? I have a 1/10th scale (first boat I ever built) that weighs slightly over 7 lbs RTR and with a proboat 1500 KV and 4s lipos it will do 45 easy

Thank you Jim.
I had read that and my current CG with all electronics is about 1.5" behind sponsons.

I have read just about everything I can on these hydro conversions.
I read a bunch of your posts back in 2003,2005 etc., with Andy Kunz (now with Spektrum) about your electric power plants for these hydros. I thought my setup is more powerful than the original KB gas and Andy was running Astro 25/5's in a similar boat. You think I can at least putt around on plane with my current set up?
Thanks
Dave in Iowa

[dpetsel]

How heavy is that boat? I have a 1/10th scale (first boat I ever built) that weighs slightly over 7 lbs RTR and with a proboat 1500 KV and 4s lipos it will do 45 easy

A little over 8 lbs 36" RTR.

[dpetsel]

Just weigh it. 8.2 lbs. RTR before the new 20"flex cable.

[Fluid]

The Dumas hydro is known to be hard to get on plane, it was designed in the 1970s (or earlier) with poor sponson geometry compared to more modern designs. The one I actually saw run needed a toss launch with WOT on the 7.5 engine to plane off...and it weighed a couple pounds less than an electric version.

OTOH since the OP already has a 1500 Kv motor he could try running on 4S and see what happens.



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[Tails Up]

Ok,never had a hydro,lots of tunnels.I didnt mean to give bad info.

[Fluid]

No problem Tails, we all learned something with this thread.


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[dpetsel]

Fluid,
I appreciate your suggestions. Since I already have the parts I am going to try my setup. I can always buy the Leo 4082.
I do have a Leo 5692 540kv with cooling jacket and motor mount that I might try to trade someone for a Leo 4082 if my setup is laggy.

[dpetsel]

Well..... I finally got a chance to take the Dumas Hydroplane out for a test at our float fly this weekend. Boat did about 45 mph. I must not have tightened the compression nut on the shaft enough because on the final run I heard it just spinning and we had to pick it up with the rescue boat. It was fun though and I learned a lot. It got up to 45 then went into LVC so I assume I need some 45-50 C batteries. It was a blast to run and will be real fun once I get the bugs out.

[dpetsel]

3rd pick was taken just before it really got out of the water.

[dpetsel]

Here is a better pic once it got on plane.