Re-Engineering A Dumas Pay'N Pak

[FloridaScaleBoater]

quit whining and finish/race something............

Jeeezzz Joe,,,,,

I thought I was the only one that "needled" this guy??

Welcome aboard!!

 

[Hydro Junkie]

Damn, you two guys are starting to sound like a person from Ohio. Give it a rest already

 

[hugh hargett]

I can wait until November or December of 2012 for the next update as I have other hobbies and other things I need to work on besides this boat since I do have a life OTHER THAN BOATS

I know thats right HJ I can relate when you say boats arent the only thing youre into. Boats bring the KID out in alot of us. You know kids cant sleep on christmas eve even in 2012 lol. Whats your weight on that girl so far?

 

[Hydro Junkie]

Right now, it's 5lbs, 4.95 oz.. I still have to finish off the radio box and around the cockpit so I figure I'll be adding a couple of more ounces before it's ready for paint. I figure I'll be doing good if it ends up under 5.5lbs. Only time will tell

 

[hugh hargett]

Whats up HJ just wondering what hp and rpm you expect out of your nitro engine? Heres that turnigy t600 mounted. Ill be going with a wire drive setup. Still havent made the move to lighten the hull yet but I will make some progress this week. Ill be watching this thread.

 

[Hydro Junkie]

I set it up with a stock NR .21 5 port with a NR version of the 3280 pipe, .187 flex cable so hopefully it's going to get 28K plus for RPM running 50% nitro. As far as HP, I don't have a clue and haven't really worried about it since the thing isn't broken in yet

 

[hugh hargett]

What size prop are you going to start with?

 

[Hydro Junkie]

I've got three Octura's to try that I had Shoboat work over for me, they are a 637, 640 and 440. If they don't do the trick, I have others to get worked over and try as well. I'm hoping to not need a lifting prop on this boat since it's wider and probably lighter than a stock Dumas would be. I'm planning on taking it out for a run as soon as I get a nice day to try them and see what happens

 

[hugh hargett]

Yes Im trying to get marks attention now but I cannot .I need some questions answered. I think hes engaged In some debate over props. It seems the weight isnt as important as the cg. People use lifters to bring the transom up and reduce the thrust angle. On my pak the thrust angle is near zero and the cg is about an inch and a half behind the sponson trailing edge.I still think the grams of weight cut away from the frame is negligible especially in my pak which is FE. Whatever gains I may have seen would have been lost as soon as I foam filled. If it were my choice to build a light version of this boat I would have done it in balsa then skinned the riding surfaces and deck with 1/16th ply. That to me would have made a big difference.You could scan your cutout frames on a scanner ,as long as the scanner is large enough, then put them in pdf's. Then you could have kevin or mike do some clean laser cut kits.

 

[Hydro Junkie]

Your CG is too far aft. It should be somewhere in the range of .75 and 1" to start and adjust from there. The only way to really know is to put the boat on the water and run it, something that mine won't get until at least the weekend due to low temperatures, rain and wind according to last night's weather forcast

In the case of your boat, having an electric drive would have let you use balsa. Using nitro, I stayed with birch ply and removed as much weight as I felt comfortable with from the framing. I figure I've taken out between .5 and .75 pounds, to me a very significant amount considering this thing was made much wider than a stock build

 

[RodneyPierce]

why do you say that balance point is too far back HJ? Its a pretty standard procedure to balance a boat at 1.5-2 inches aft of the sponson back.

 

[Hydro Junkie]

On a scale or sport 40 hull, I would agree. His boat, pictured on page 3, has the stock bottom profile with the bottom break right at the sponson transom. To be balanced that far aft with all the lift forward is asking to have it blow over. What you have to consider is the boat is 30" long and has a 17" afterplane, so that means it's presently balancing with the CG almost dead center. All I'm suggesting is that he try to move the CG ahead so he can fine tune the balance with his battery packs and radio gear later without having to add weight in the sponsons. Something else you also have to consider is his boat also hasn't been skinned yet so the CG is going to shift further aft, especially if he's using the stock radio box location, aft of the bottom break, and more so when the cowl and wing are installed. All that being said, his boat is going to be very different than mine, his being electric while mine is .21 powered, not to mention the fact that my sponsons were cut shallower by 3/8" and the bottom break moved aft 8.5" so who knows how they will react when pushed, I'd rather play it safe

 

[hugh hargett]

I will have a place for some ballast up front but it wont be a problem to move the battery an inch forward. That should do it. I think a balsa boat skinned with birch and carbon fibre epoxy laminate on the floor would withstand a hard season of nitro racing. Even with the birch in enough time you will get stress cracks in the tub. Kept the material I cut away so far. 11.9 grams apprx .027 pounds lol.Even with all the material widdled away it will never reach a 1/4 pound of savings, but it will allow you to add strength in the neede places without adding weight.

 

[hugh hargett]

Hj whats next?

 

[Hydro Junkie]

a day or two at the mill making a servo mount and then finishing the radio box. After that, it's testing and continued breaking in the engine. Had other things to work on so the boat has been put on a back burner for a bit

 

[hugh hargett]

Wat going on with this build HJ?

 

[Hydro Junkie]

Picked up a driver at the hydro show last weekend but otherwise not much due to work