ML Boatworks GP-400 Build

[Dasboatman]

Hey Phil,

I though you had told me you started that hull about 1978. 1990 - just a youthful contender.

I figured I'd bust your chops because I know you have a thick Hide. Har, Har !!! Consider it Pay Back for the "Brand X" comments over the years. I certainly have no desire to provide kits or hulls to anyone. I build a few hulls for Friends that are racers, and there are a few of mine that others have ended up with that I gave to Friends. Human nature being as it is, I prefer to run my old hulls through the band saw rather than selling them to anyone. I have seen very competative race boats turned into complete garbage in the hands of others.

In support of Mike, I have only one thing more to say. We had an old cook on one submarine I served on. His favorite line was: "I may have to take your ****. You - have to eat mine."

CHEERS !!! Bob

 

[anthony_marquart]

I am building a wooden sp40 boat from mike,.. that has a similar design as the GP400. I don';t have the tops on the sponsons yet. Should I put some lead in the left sponson tip before I close it up? if so,.. how much?

 

[RodneyPierce]

Anthony, perhaps make a hatch panel that you can just tape on and then you can add weight to it as needed?

 

[FloridaScaleBoater]

I am building a wooden sp40 boat from mike,.. that has a similar design as the GP400. I don';t have the tops on the sponsons yet. Should I put some lead in the left sponson tip before I close it up? if so,.. how much?

Anthony,, the answer to your question,,, NOW,,, NOT YET.

Since your hull is still in the "being built" stage,,, you have now way of knowing where it will balance out at.. Why add weight if its not needed?

Once you hull is built and rigged IE: Everything installed where you want it.... and I fill my gas tank 1/2 full and check for balance. my rule of thumb (through experienced builders) is to have your hull balance about the middle of the turn fin,, maybe, slightly nose heavy, also look at you port, to starboard balance (also very important) If weight is then needed, bore a small hole on the inside of each sponson tip and mix a "slurry" of BB's (of the determined weight) and epoxy and pour this into the holes, leaving the hull resting bow down,,, then fill your holes W/ filler, and cloth and test run.

Just MY way of doing this,, I'm sure there are many other ways too

 

[anthony_marquart]

I understand that I don't know where it will balance.. just thought it might be good to be proactive.. If I know Ill be adding some,,, maybe I could do it now.. but I will wait.

 

[Bert Dygert]

Anthony,

As Mike and Don have done. Run the boat then add the lead to the sponson tops or sponson wall. Get the fuel tanks as far forward as possible. I would put the engine as far forward as possible also. Maybe even mid ship radio box behind the motor??? The engine and the fuel are the two heaviest items in the boat. That way you will reduce the lead weight if needed.

Mike, What do you think?

Bert

 

[Mike Luszcz]

Bert, i definately agree. One other thing i do, is take my unbonded decks, hardware, motors, batteries etc. Place them in the areas they go, and see how far off i am. If i am close, i add no hidden lead, if its really off, i put some in to get it close.

 

[JimStephens]

Guys, mostly a reader, but thought I would jump in. I only race FE and am new to the sport of racing (finishing second year) four years running them. Hearing each person's ideas and Mikes discussion on the thought process that went into the design has been really educational. Mike don't take it pesonally, because each person is going to take your boat and tweak to their thought process. The best you can do is as you suggested, which is here is the setup I know that works and you should give it a try. You are providing the most extensive set of kits and boats out there and we all value this selection. I also am happy that we have a new set of race hydro's to try out so we don't end up with just a bunch of whips and PT's out therez(I run those too). The variety of boats racing is also what makes it fun and interesting.

I do have Mike's gp335 and am going to start setting it up over Thanksgiving week. With this boat we will have no less than THREE of these guys racing in P-Sport Hydro here in Houston in December. Says something good about the design.

Keep building Mike!!!

 

[Ben G.]

Just a setup note on the lighter side. For the SAW application, as measured on the bench: 0 degree tub, CG 7/8" back, strut just slightly deeper than sponson depth, AOA 3.43 degrees, strut neutral. The GP265 ran stable with no hint of blowing over.

It is important to mention I was running a higher lift prop, so a little deeper on the strut for less lift props is probably appropriate. Remember that I'm working with a limited data set at this time. The only reason why Mike's GP265 didn't get the record was that I ran out of RPM with my given setup and didn't have time to swap the motor and adjust for the different weight of that motor. If I had had the time to swap the motor and run the different prop I wanted to, it would have been no problem since it ran very stable. I could add some rudder at speed without unsettling everything and she was just slightly on the wet side of things (as needed for SAW to ensure two passes including one typically into the wind).

I did experience hop when inducing slightly less lift in the prop (modified to redirect lift to thrust), but can be directly attributed to a little negative in the strut. Once put nearly neutral, the hop disappeared and ran flat again.

I see no reason why the model doesn't work, at least in the GP265 scale. For an oval application, a different set of parameters are at play, such as AOA, but presently, the hull is neutral at speed. Everything else depends on your specific setup down to the simplest factors such as prop choice and RPM.

 

[Bert Dygert]

Update 11/17/12,

I had the boat out Saturday. The nitro hull perfers three blade props. The two blade prop carrys the left sponsons off the water in the straight and at the end of the straight it packs enough air under the hull to create a left sponson blow over. I had an half ounce of lead on the sponson tips. After the blow over I added and ounce and a half( 35 grams) of lead to inside sponson wall at the tip and changed to X450 three blade. No more torque lift on the sponson. The boat ran very well. The motor was running out of prop so I moved up to a stock X452 three blade. The engine like the bigger load but sags just of a second on acceleration out of the corner. The boat had good straight away speed. So I have done some prop work to the x452 three blade to mirror the work done on the X450 three blade. Hopefully the weather will hold out for Friday for the last testing of the year.

We had a video camera out with us but it was to grainy to see how the hull rides. Sorry.

I put on a Virginia Craftsmen Sport 40 turn fin and dialed half the rudder throw out because of over turning. That skid fin is the ticket. not sure where the one I had on the boat came from now.

Bert Dygert

 

[Mike Luszcz]

That sounds like progression! Did you make it back out last friday?

 

[Bert Dygert]

Mike,

I didn't get out last weekend. The work thing wrecked my plans but the weather went cold and snowy too. It looks like this weekend is the last run for the season. If the weather holds 50's on the weekend and 60's on Monday. I feel a sickness coming on.

Bert

 

[Mike Luszcz]

Snow? Lol, whats that???? haha

 

[Bert Dygert]

Mike and guys,

I had the boat out over the weekend. The boat is fast but when the fuel load gets down to about 4 ounces the boat carries the left sponson off the water and then with the help of a slight wake the boat lifts and rolls right and blows off.

The fix is in process. I have moved the engine about three inches forward and reduced the radio box to less the four inches deep ( front to back). I will also move the fuel tanks foward a couple more inches. This should help with the lifting of the hull and move the CG further forward.

Any thoughts about off setting the strut to the left to reduce the canlever effect of the prop and help with the torquing of the left sponson?

Bert Dygert

 

[anthony_marquart]

I am finding that I need to place my engine pretty far forward to get the CG around 1-1.5,.. let me know where your CG ends up please.

 

[Bert Dygert]

Anthony,

It's going to be a few days. I have to order new aluminum stock and re-engineer the motor mount to get around the sponson transom bulkhead (it's right in the way I'm going to bridge it with the aluminum engine rail). The CMB HR (slant carb.) mount will allow the motor to move further forward than the VAC becuase of the carb. clearance.

Bert

 

[Bert Dygert]

Anthony,

I measured the cg last night. Right now without the pipe installed the CG is 1.1875 behind the sponson. With the new engine postion I have to make a new cowl that has to be higher for the VAC motor. The engine case is setting forward of the transom bulkhead but the flywheel is setting just behind. If you want the engine further forward then you will have to give up the front radio box and make it mid boat. I will post picture soon.

Also I moved the battery to the left side of the hull as far foward as possible to help with the prop torque on the left sponson causing the blowovers.

Merry Christmas

Bert Dygert

.

 

[Bert Dygert]

Here are some updated pictures with the new radio box and motor mount. Note the old motor mount holes are about 2.5 inches behind the new motor location.

BerT Dygert

 

[RobertWurster]

looking good hope she runs good for you.

 

[Jim Caldwell]

Where is the CG now??