HELP NEEDED WITH SET UP FOR 1/8TH SCALE HYDROPLANE MHR 8255

HI Guys,

I have an electric powered ML Boatworks 8255 1/8th scale hydroplane powered by a TP 4070 880kv motor on 10s1p lipos and am having problems with the hull. The driveline is offset to the right 1/4 of an inch looking from the back and the rudder (sport 40 square rudder) has been tried both on the right side of the hull and now the left side. Driveline was offset due to turn fin and rudder being on same side of boat. I have used 447/3, x450/2, x452/2 props without any success. The boat now has a 1/2 inch by 1/2 inch airdam under the hull. Strut is a flat bottom and set 26mm below bottom of hull and flat. ( no negative or positive angle.)

The problem is the boat is very unsettled and basically flighty even in smooth water conditions. If you drive it flat out it will blow over down the straight away, even with the batteries as far forward as possible, however if it hits another boats wash and gets airborne it always lands front first which is telling me there is too much weight forward but I need the weight there as it blows over down the straight.

Questions:

Where should the C of G be for this hull?

How do you get the hull to sit level left to right sponson wise with 10s packs jammed 1.5 inches off centre to the right due to the offset tub?

Rudder best on left or right?

Strut depth?

Is there anyone racing these successfully in electric form?

All help is greatly appreciated.

Thanks

Trev

I would get the turn fin parallel to the bottom. Lowering the strut should raise the rear of the boat, less angle of attack and lift. Extra weight should be to the left to counteract torque. Cg around 1.5" from the rear of the sponson. Keep us posted on the progress!

Trevor,

When I have time, (next couple of days) I will sit down and type out some "thoughts" for a possible cure.

Put some negative angle in the strut to get the rear of the boat up when in the straightaway. If it is flighty in smooth water, this has to be the issue. Could also use a lifting prop like a 1455/3. Any 1400 series Octura will help.

Hi,

Thanks for your replies guys, will look at different props and strut angles.

Would really appreciate that FLORIDA SCALE BOATER if you could do that for me.

Thanks

Trev

ask ML for advice.

phil thomas might provide set up instructions for his 1/8 8255

dave frank 1/12 scale 30 inch 8255 sport hydroplane drawing for reference

you might consider removing the long air trap under the after plane if it's on your hull

your build looks beautiful.

what paint scheme is that ?

please post photos of entire boat top and bottom

Oberto_1.pdf

Oberto_2.pdf

Hi Dave,

Thanks for the drawing as a reference, I notice it doesn't have the offset tub which I think is good. I still believe my offset tub is causing a lot of my issues, hope I am proven wrong.

My boat club here in Brisbane, Australia has opened up the paint schemes to be whatever you wish, so I always have liked yellow and decided to come up with my own design and name.

Attached are a couple of pics you asked for.

Thanks

Trev

Try this.

TREVOR JENSEN said:

Hi Dave,

Thanks for the drawing as a reference, I notice it doesn't have the offset tub which I think is good. I still believe my offset tub is causing a lot of my issues, hope I am proven wrong.

My boat club here in Brisbane, Australia has opened up the paint schemes to be whatever you wish, so I always have liked yellow and decided to come up with my own design and name.

Attached are a couple of pics you asked for.

Thanks

Trev

Click to expand...

beautiful boat. thank you for photos.

notice the notches on the bottom inboard and outboard edges of sponsons

in the Dave Frank drawing.

here's a 43 inch gas version with the long air traps. no blow offs.

need help turning photos right side up

good luck

My opinion is this,

The hull has TOO much ram wing (forward end of center section) bottom.

Where you have added to piece of wood to break up the air.

You will need to fill in that upward slope in the bottom. use balsa wood, foam and sheet with 1/16th ply once formed.

The balance point should be right down the middle of the turn fin (this will NOT make a difference) at this point! you must fix the bottom first.

Also, the turn fin, a VERY knowledgeable hydro builder once told me that the front, bottom edge of a turn fin being squared will cause lift.

How many guys run struts with no angle? Yes, if you can design the perfect hull to carry the weight, have the fuel on the center of gravity, figure out the density of air under the boat for different temperatures and altitudes, then you might be able to run the strut with zero angle. This will give you the ultimate speed. Even riggers need downforce and run 1-2 degree's of negative angle. I would try this before glueing and sheeting the bottom of the hull.

Have you tried to put negative angle in the strut? Have you tried a "lifting" prop? The X series props have alot less lift than a 1400 series.

I think your missing the obvious.

Even full scale unlimiteds run negative angle as it helps to get the rear of the boat off the water resulting in more speed.

Mike L. ML Boat Works PLEASE DO NOT TAKE THIS THE WRONG WAY, I think you have done exceptional work for our RC boating community and offer some awesome kits.

Rob,

I'm sure you have run against Rob Betke from you neck of the woods,

I ran with him in Evansville a few years back and was amazed at how his boat ran, when I found out it was an ML kit boat.

He then showed me the bottom of his boat.

Yup, just as I have explained above. The ram wing had been filled in forward and the boat was perfect ALL WEEKEND long

FloridaScaleBoater said:

Mike L. ML Boat Works PLEASE DO NOT TAKE THIS THE WRONG WAY, I think you have done exceptional work for our RC boating community and offer some awesome kits.

Rob,

I'm sure you have run against Rob Betke from you neck of the woods,

I ran with him in Evansville a few years back and was amazed at how his boat ran, when I found out it was an ML kit boat.

He then showed me the bottom of his boat.

Yup, just as I have explained above. The ram wing had been filled in forward and the boat was perfect ALL WEEKEND long

Click to expand...

Does he run his strut perfectly flat and parallel when the hull is level? If so, then he has the perfect set up. I have yet to see a sport boat with the strut set at zero degrees and stay on the water in racing conditions.

I'm out west and maybe we are doing it all wrong, lol

I just thought that trying negative angle and a lifting prop would help. The original post states flat strut with no angle. If the hull is packing too much air and not letting it escape (this is where rear hull up with strut angle), then it needs a design change

I concur with Robs advice, start with the simple before you start major hull mods at this point and only one change at a time.

1. Add some negative strut angle,see what happens.

2. Prop design and lift is just as impactful, see what happens.

You may not be so far from the sweet spot as you think you are, find that sweet spot and it may fly into the wind just the way you want. I've found just about every hull to be slightly different and the fixes are unique to each.

3. Hopefully you have a few turn fin designs, try swapping a couple and see what you get. As already has been said, make sure the fin is not adding unwanted lift to the nose, you want it cutting the water perfectly.

4. As for which side the rudder is on, I have always had good luck with it being on the opposite side of the skid fin. Some people will run them same side with luck but most will recommend it be on the opposite side and avoid the hole created by the skid fin.

5. Check CG front to back, make sure it's right behind the sponson like others have said already, you get it too far forward or back will create flight tuning challenges too. Get it as close as possible, then tune around it with strut angles and props.

Failing all this, you should be close, toy with some temporary bottom fixes to give you confidence in further hull mods before you head down that path.

Hope this helps.

FLORIDA SCALE BOATER- pm sent.

Thanks to all that have replied, a lot of testing with a vision of what areas to test has been greatly appreciated.

Thank you all

Trev.

Lots of good advice above. My 8255 was a Dave Frank design and ran very well both as a nitro boat and an electric. It still holds the T sport hydro and 1/8 scale electric two lap records. I also had a Phil Thomas 8255 and that hull has a very different bottom configuration. The needed strut length is quite a bit longer. For my thoughts on the subject see the NAMBA articles Electrifying Adventures in Scale in the November 2012 Propwash and Its the Breaks in the April 2013 Propwash both at NAMBA.com under News.

Lohring Miller

First rule- change ONE THING AT A TIME. That's the only way you'll know if change works or not. And personally I'd start with running the strut deeper...........

Duck899 said:

How many guys run struts with no angle? Yes, if you can design the perfect hull to carry the weight, have the fuel on the center of gravity, figure out the density of air under the boat for different temperatures and altitudes, then you might be able to run the strut with zero angle. This will give you the ultimate speed. Even riggers need downforce and run 1-2 degree's of negative angle. I would try this before glueing and sheeting the bottom of the hull.

Have you tried to put negative angle in the strut? Have you tried a "lifting" prop? The X series props have alot less lift than a 1400 series.

I think your missing the obvious.

Even full scale unlimiteds run negative angle as it helps to get the rear of the boat off the water resulting in more speed.

Click to expand...

I'll disagree here. I've run many scales over the years with zero strut angle BUT spent plenty of time on overall set up. The only riggers I ever ran that needed negative on the strut were Eagle SGs. All my current riggers run flat (zero angle) struts. I would look real hard at strut depth first...........

After viewing the LohringMiller boat in the NAMBA propwash I notice the tub area is much wider and no real sign of a offset tub so batteries can be evenly spread out in the hull.

Can you somehow convince me that 1.5kg of lipos suitated 1.5inches to the right of the centerline of the hull isn't apart of causing my issues with too much weight on turn fin side of boat.

Thanks

Trev

TREVOR JENSEN said:

After viewing the LohringMiller boat in the NAMBA propwash I notice the tub area is much wider and no real sign of a offset tub so batteries can be evenly spread out in the hull.

Can you somehow convince me that 1.5kg of lipos suitated 1.5inches to the right of the centerline of the hull isn't apart of causing my issues with too much weight on turn fin side of boat.

Thanks

Trev

Click to expand...

Sounds like you've already convinced yourself. You are comparing different boats and what works on one may not work on the other. At the risk of repeating myself start with a strut adjustment. What is your sponson depth at trailing edge? What is your strut depth from hull bottom to shaft centerline?