ML Boatworks GP-400 Build

[anthony_marquart]

where did you get that rudder pushrod?

 

[Lay26]

dave brown products from tower http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXB901&P=ML

 

[RobertWurster]

That kit is what im using just drill out the hole if using 440 rod,I got my Arrow shaft from wall mart .

 

[Bert Dygert]

Progress Report

Here are the lastest pictures. Almost ready for the pond tomorrow.

Enjoy.

Bert

 

[longballlumber]

Nice looking build Burt.

Later,

Mike

 

[JohnOttosen]

Looking forward to video.

 

[Lay26]

what carb is that?

 

[Bert Dygert]

Guys,

Report from the pond is the hull is fast and runs very lite. Strut depth is critical on the hull. Right know I am running the strut at 1.20 inches deep. It need to go a little deepper to keep the hull flat on the water. The left sponson is light on the water as well. I had to put 6 ounces of lead in the front of the raddio box to help stabilize the hull.

I am going to flip the fuel tanks around to move them further forward and put more hook in the skid fin. Picture will come later today.

Henry, thats a OS 40 A I adapted over for the HR motor.

Bert Dygert

 

[Mike Luszcz]

Bert,

What fin are you using? Could less weight be used if it was put up in the tip of the left sponson? You are right, strut depth is very critical. Flat bottom or round bottom strut? If you are at 1.2" then you are still shy of the sponson heal depth by 1/16". I ran mine 1/8" deeper than the sponson heel depth. I would add another 3/16" depth. If the tail is dragging you will be adding positive angle in the pan, and it will be light on the water. I was also running an X457 with round bottom strut, you may be using something else.

How fast do you thing it was running in the straights? Did the flat bottom strut (if I remember right you told me you might use one) cause any choppiness in the turns? Where is your CoG?

Ben G. up in Virginia ran the GP265 at the SAW trials this weekend with a 2s setup and got above the 70mph mark with his first time out with the boat. He was tail dragging at first, and once the bottom due to strut depth was leveled out those issues got a lot better. He is going to try again in April as he ran out of RPM to get to the 77.xx mph record mark he needed.

Let me know, sounds like you still have some work to do, but it would be doable! Mike

 

[Mike Luszcz]

I talked to Bert in PM, and found out his CoG was 3" behind the sponson heal, and his overall strut depth is around 5/16" shallower with that strut and prop setup he has currently. Those two factors I think are key to why the boat is light on the water, and why the left sponson is lifting. My gp400 had cog around 2"- 2.25" behind sponson heal and was still loose but I had more overall weight. The strut was much deeper, and at 65-70mph as long as you were not jamming it left, would hold on the water fine, and the back end of the boat was up and level, which is key, because if your tail dragging, then you are creating positive pressure in the tunnel, and it was designed to have that rear end up to keep it flat on the bottom.

From what has been learned in high speed saw testing is shallower sponson depth, which I was asked if it would help to reduce sponson depth to reduce the amount of air, which from what I understand is a common missconception, will only make a blow off problem worse. All tests point to deeper sponson depth removes that pressure, stabilizing the higher speeds. I had a lot of racers call me during the GP series design, and said get those sponsons deeper!!! They begged I do that.

3" is just way to far back on CoG...that is making a bad situation worse. Any other boat out there would have the CoG at 1", and while this boat does great even at 2"...I think 3" is getting to the point of pushing its luck! I want to say you might need to get it back to 2" behind the heal. The tail dragging, and CoG is the reason the hull is so light..and its causing the left sponson to lift as well. Do what a fellow racer did to his scale this last week...First, use some flat lead weigh and lay it on the sponson tips to determine where you need to be to get the CoG @2", then get some #8 or #9 lead shot, drill a small hole on the inside edge of the sponsons, and pour in the shot to the amount you need, then pour in some epoxy to hold it in place. This will reduce overall amount needed, and get that CoG forward. Remove the 6 oz. in the radio box first tho, as its not going to help much that far back. I think the current setup is just leaning to much on the back of the boat...This was the same situation Ben G. with his GP265 was facing. He started at 2" behind sponson heal, then brought it up to 1"..on a 26.5" boat and stability went way up...so I know you need to get further forward.

I pm'ed this back to Bert as well, but this is not the first case I have seen out there, some FE guys are running there CoG a little to far back, or the strut depth to shallow, and I myself did the same thing at first. Once I listened to some other guys in the know, and deepened up that strut depth..wow did things change! I just wanted those reading this to know as they may experience similiar problems, and I want everyone on the right path from the start! Because this series of sport hydros has a lot of different things going on than most of the other boats out there, its just about certain throwing out old standard depths or ideas might be needed.

Keep us posted Bert...you will get there with the setup, and you will have it running like you want! Mike

 

[RobertWurster]

Mike what is your thoughts on running the rudder on the right? I see in your build on the gp boats you put them on the left.

 

[Mike Luszcz]

I do believe, now that I have been told why, that the rudder on the right is the correct way to go...and with a proper setup, should help keep the left sponson down when turning left. Good question! Mike

 

[RobertWurster]

Thanx Mike.

 

[Bert Dygert]

Guys,

Here are some pictures from testing. Note there is a progression of changes that occurred with each run.

Bert

 

[Mike Luszcz]

Tail doesn't look bad, its the CoG that you will need to work on first. I have also found in the super calm water like that that boat is looser than race water. The chop definitely keeps the air bled out!

 

[Mike Luszcz]

I forgot to mention, Doug Shepard called last night, we spoke for about an hour! I finally realized yours and his thought process. I did not realize it, but apparently at the proper angle of attack on the whip 40, the pan has like 3 degrees negative, so you can run a shallower strut with the tail down, and the boat is fine.

With this one, for the proper AoA, your pan will be at a level run angle, if its tail dragging, the AoA could be 4-6 degrees, but when the pan is good and level the AoA is 3-4 degree (can't remember the exact number off hand). So from what I understand you guys were thinking my pan was built with a 3 degree negative pan, and were worried about running the pan at 0 degrees thinking it wouldmake AoA 1-2 degrees based on prior experiences with other boats and their pan design. Hope that is understandable what I just wrote. But Doug understood where I was going with it. Mike

 

[Bert Dygert]

Mike,

The second picture tell the story best. Ride attitude looks pretty close. I will work on moving the CG closer to the transom for better turning. I rebuilt the tanks last night to turn them around moving them forward about three inches.

With the strut deeper than the transom of the sponson your effectively running the pan at a negative angle of 0.6 degree's. Also robbing the AOA on the hull of that 0.6 degree's unless the bottom is designed to run negative (transom higher than sponsons). Also the prop is going to lift the rear of the boat as it unloads creating extra less AOA.

Bert

 

[anthony_marquart]

Is there an issue with running the tub flat on a sport boat? I thought the design of t his boat was to run level. That would mean running the xseries below the sponson transom,.. and maybe a lifting prop level with it.. right?

 

[Mike Luszcz]

Bert, In theory, if water was a hard surface, and there was not drop at all in the transom then yes, you would have negative in the pan, but the weight of the boat alone will force the transom to drop in the water while running at least 1/8". You are also running a prop that is 5mm total smaller than the one I was using, or 2.5mm per blade. I think with your current adjustment of 1/8" deeper on the strut, and your prop diameter, you are looking at just a slight drop in the transom even after this adjustment. I don't know as your total weight is different than mine was, so its going to be a game of getting out there and fine tuning the depth. I do believe you will now be in the ballpark once the CoG is adjusted. Just use this adjustment to see where you are at next time in the water, and go from there on strut depth, or CoG. Just for comparision, my gp400 ready to run weight was 12.5 lbs. I suspect you are at 9-10lbs? You are definately the crash test dummy for this boat on the nitro side of things! You will get it running how you want it tho, just keep working on it!

Anthony, yep, this boat is designed, so that when the pan is at 0 degrees while out on the water, your AoA will be in the 3.5 degree range. Now, water conditions will dictate weather its 3.0 , 3.5, 4,0 degrees, etc. Its one of those things, nothing is going to stay at a perfect dead angle on the water..its just not possible. Waves and wind will move the boat up, down, and around...nothing we can do about that. But getting the boat as close to its design as possible is key for it being stable as it transitions threw that up, down and around scenario!

And yes, a lifting prop will probably require less strut depth, however Bert is running an X series right now, as was I. I still don't buy into the lifting prop thing. To me, if your prop has to do lifting, you are loosing efficency as you are not only asking the prop to push water towards the rear for propulsion, but you are also asking it to lift the boat. That is taking power away from where it counts. Is that true, or a big factor..I don't know. Someone like Andy Brown would know more than me, but I think its an educated guess! haha.

 

[anthony_marquart]

I guess time will tell with this prop thing. Some guys have told me to run a 1440 or 1445, some guys x-series,.. some guys ABC,.. we will see though as testing time accumulates!