Unknown 80's 42" Mono quest for high speeds

[LibertyFrancis]

I acquired this mono through an estate sale. It seems to be a bit of a mystery who makes this hull but its fiberglass and the hatch fits poorly. I know that much.
In 2021 I started a built on this boat for my 11 yr old son and quickly dropped $600 in electronics, stinger, rudder, etc into it and realized maybe this should remain dad's toy boat.




The initial build was a TP4070 (1700kv) motor and SeaKing 180a ESC with a octura X447. I had modified the prop and was able to get the boat up around 60mph on 6s with terrible handling.
I was certain this boat hull just was not good for speeds above 60 mph. I don't see new hull designs having the strakes run all the way back and its just outdated compared to what I see with new boats.

On the first FE build for this boat, I had put the motor and ESC towards the front and the battery mounts were near the rear.




The boat sat through most of 2022 I did some prop testing and found which prop the boat likes best (Dasbota octura prop) but ultimately the setup just didnt feel safe to go faster.

This year 2023 I decided to change the layout and try it again.
I changed motor KV (top secret) but it is still a TP4070, moved the motor back 190mm, used the better OSE quick change motor mount, and the XLX2 ESC. All of these were parts borrowed from my RC cars so I didn't have to repurchase any of these large ticket items $$$. The LiPo now resides in the front on an OSE carbon fiber battery tray.

The boat still needs a significant amount of trim tab to my surprise, but it's running much faster now.
It is not pretty... I know but it gets the job done. The transom looks like swiss cheese at this point with all the epoxy filled holes from various setups over the years, but she runs good and fast!



My goal is to push her into the triple digits and see just how far I can go with that. If I can, I'll stay on 6s just because that makes it more impressive!
Next time out I'll be sure to get the GPS/phone screen more visible.

 

[LibertyFrancis]

Thought I'd share some interesting data pulled from the XLX2 doing some 4s testing on this 42" mono.

This was part of my testing in 2022 with the old layout which tended to run very dry. All of these runs were on 4s in the 45-53 mph range.
The X645 is a dasboata prop and it shows as the most efficient of the bunch. The X447 I had re-worked down to 45mm and added pitch. I'd estimate it was very similar to the X645 when all was said and done except I was not able to make it as good as Chris's prop. All of the rest were only balanced and sharpened.



You can see here Chri's X645 prop pulled only 115 amps at peak speed going about the same speed as the other props.
Pulling lower amps means you can retain more voltage and that shows with the RPMs at peak speed also.

On higher power like 6s the lower amperage draw becomes very important!

 

[Bret Muldner]

As long as your having fun it doesn't have to be pretty! Even better if your kids are around...

 

[LibertyFrancis]

Tried shortening the rudder yesterday and the result was terrible. (Clearly, I went too short)

The boat was pulling hard to the right and took almost full left steer to keep the boat tracking straight.
I was hoping to reduce drag but not worth it.

 

[LibertyFrancis]

I was able to get back out and test with a longer rudder and that resolved the issue.
Unfortunately while trying to launch the boat the rudder caught the end of my inflatable paddle board and put a nice 6-8" cut in it, taking out my boat rescue vehicle.

No more high-speed passes until that gets replaced or repaired.

 

[LibertyFrancis]

Took the mono out this weekend and trying to get it back to its former glory.
Didnt have enough trim tab in the setup and it blew over at 75 mph. Luckily it landed right side up and was able to drive it back!

Then my rigger must have hit something in the shallow spot (need to investigate the pond depth)

 

[LibertyFrancis]

The front of this boat could use some help with keeping the nose down at 90+ mph speeds. The facelift plastic surgery nose job has begun!
The idea here is to counter act all the surface area catching air and pushing the bottom of the boat up. The top surface will get angled down hopefully helping to balance the airflow some (although not completely)



On a side note, I guess now it has become a 40" mono as I'll have to shorten it some.

 

[Peter Wibe Enevoldsen]

im very interested to see how this turns out!

 

[LibertyFrancis]

Cutting the boat up is a bit nerve-racking, but interesting too.
I am always shocked at how thin these hulls are. It seems to be mostly gel-coat with a tiny bit of fiberglass. There can't be more than one layer of fiberglass there.

I had used the total boat 2 part flotation foam (2 LBS density)
This stuff hardens like a rock!!! I am certain it helps hold the boat together during those nasty 80+ mph crashes.

It is pretty hard to get it out but as you can see I was able to clean up the front end removing most of the foam so that I can re-bond the nose.
All in all with the new angle it removed about 2" of length.


I figure while the boat is going under the knife I am going to re-make the hatch cover also.

 

[LibertyFrancis]

So far I have been running a 3/16" flex shaft.
The 90 mph run at peak speed was outputting 9.36 kW (6s LiPo setup)

I'm pretty certain I am pushing the limits on that small flex shaft already. If I can go faster with higher voltages I'll likely need to upgrade the driveline. The trendline on the data indicates 100 mph will need 12kW and 110 mph will need approximately 14kW.

Some of my friends like to tease me about tracking data in excel spread sheets but the data can tell you some great information

 

[John Finch]

Let your buddies tease you. You are a step ahead by knowing the numbers and how they relate to each other. My xlx2, recommended by Tyler has proven awesome with the data I have retrieved from testing. I have found some pretty interesting things that make the difference between pulling 400 amps vs 250 amps with only one change in setup. Awesome tool. When you keep the amp draw down you can swing more prop and things stay cool!

 

[LibertyFrancis]

Let your buddies tease you. You are a step ahead by knowing the numbers and how they relate to each other. My xlx2, recommended by Tyler has proven awesome with the data I have retrieved from testing. I have found some pretty interesting things that make the difference between pulling 400 amps vs 250 amps with only one change in setup. Awesome tool. When you keep the amp draw down you can swing more prop and things stay cool!

Thanks John!
I have not figured out how to reduce the amperage that much yet, but working on some things
That would be amazing if I could get the amperage that low while remaining stable and now blowing over.

It is funny that I have a rigger that can probably do 120+ MPH right now, and as a speed junkie that should be what I want.
However, I now find myself most interested in spending time on this mono hull due to the technical challenges it provides.

 

[LibertyFrancis]

The front end has been epoxied back together. It also has both a layer of fiberglass and 2 part flotation foam to help hold it all together.
While working on the boat I decided to change the hatch cover. A large piece of fiberglass sheet was annoyingly expensive and I don't want to use CF because it blocks GPS signals... I decided to just make some out of chopped strand mat and poly resin that I had already.

To make it smooth and flat I waxed a piece of metal and wet out the fiberglass on top of the metal to provide a slick finial surface (at least what will be seen on the top side)
I had mis-judged how big the hatch was going to be and didnt wet the fiberglass out far enough. You will noticed the edges look dry near the drawn lines.
I re-wet them afterwards but it is just not the same and is not flat/smooth.

Determined to make it work today I am coating it in gelcoat so the hatch is a smooth surface that hatch tape will work well with.

 

[K F Wheeler]

I've always been a fan of aerodynamics. Anything that may have any affect on attempting faster travel of anything... That being said... John Finch did an article on pushing a mono hull to higher speeds. You may or may not know about that article. In any case it's well worth reading. And, if you've read it before it's worth reading again! I have to admit some of what he found surprised me more than once... It's in Advanced R/C Boat Modeling. Published in '92 and republished in '94. Sorry, I am NOT a fan of mono's. But, I found this well worth reading! Chapters one and two.
Thanks, John!

Ken

 

[Peter Wibe Enevoldsen]

I love where this is going! Keep up the great work.

 

[LibertyFrancis]

I've always been a fan of aerodynamics. Anything that may have any affect on attempting faster travel of anything... That being said... John Finch did an article on pushing a mono hull to higher speeds. You may or may not know about that article. In any case it's well worth reading. And, if you've read it before it's worth reading again! I have to admit some of what he found surprised me more than once... It's in Advanced R/C Boat Modeling. Published in '92 and republished in '94. Sorry, I am NOT a fan of mono's. But, I found this well worth reading! Chapters one and two.
Thanks, John!

Ken

Yes, I have read through some of Johns's articles and agree his contributions are very helpful.
He and I talk often.

I love where this is going! Keep up the great work.

Thanks Peter!

 

[Wasted wages]

I was told once by a full size boat engineer
with Volvo Penta that once the critical speed of a common mono hull has been reached, it requires like double the horsepower to gain only a small percentage more speed...

Don't know how true this is, but seems plausible due to the hydrodynamic forces involved in the surface area of the wetted surface.. which is why you see stepped hulls. Less drag.

Of course full size doesn't always equate to our small boats, as evidenced by our boats blowing over as the speed goes up.

If full size commercial boats blew over with the frequency of our little boats, there wouldn't be any boat builders left on the planet..

 

[LibertyFrancis]

I was told once by a full size boat engineer
with Volvo Penta that once the critical speed of a common mono hull has been reached, it requires like double the horsepower to gain only a small percentage more speed...

Don't know how true this is, but seems plausible due to the hydrodynamic forces involved in the surface area of the wetted surface.. which is why you see stepped hulls. Less drag.

Of course full size doesn't always equate to our small boats, as evidenced by our boats blowing over as the speed goes up.

If full size commercial boats blew over with the frequency of our little boats, there wouldn't be any boat builders left on the planet..

Agreed and there gets to be a point where you can only throw so much power at it...
I am going to try a few things to reduce the drag but ultimately.... I might have already found the maximum speed for 6s with this setup.

Thankfully we got some decent rain yesterday. All the ponds were nearly dried up and had me worried about dragging the rudder on the bottom.

 

[Wasted wages]

The speeds your trying to achieve is such a delicate balance of many factors...
Drag, lift, weight, water ripples, wind, power, COG balance, prop, and many other factors all play into the perfect pass.

I wish you well in your endeavor, would love to see you make a record pass at a national event with actual timing equipment...

 

[LibertyFrancis]

The speeds your trying to achieve is such a delicate balance of many factors...
Drag, lift, weight, water ripples, wind, power, COG balance, prop, and many other factors all play into the perfect pass.

I wish you well in your endeavor, would love to see you make a record pass at a national event with actual timing equipment...

I think I may try to next year. This year it is just not likely to happen.
As far as I am aware the only SAW event near me is in Huntsville Alabama. Does that sound right?
(currently live in Dallas Texas and might be moving to Memphis Tennessee)