Crusader.

[785boats]

Here are the rudimentary beginnings of John Cobbs' Crusader. The next boat in the line of 'World Water Speed Record Boats' that I'm building.

Again in 1/8 scale like the others. So a total length of around 46".

I'm not confident that the EDF will work in this one because the inlets are even smaller in proportion than the Spirit of Australia that I've just completed.
But I'll make them bigger & open out the cockpit as an air inlet so we can give it a damn good crack at working with an EDF.
I've got no problems with converting it to a prop rider if the EDF doesn't work.
Here's some photos & information on the original boat for those interested. I find that researching a project can be as much fun, and certainly as interesting, as building & running a boat.
A Canard design in 1952. Love it. But a tragic end to a pioneer in water speed record attempts.

https://www.google.com.au/search?q=John+Cobb+Crusader&rlz=1C1WPZB_enAU728AU728&espv=2&biw=1664&bih=902&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjh3PK92JvSAhWONpQKHTi2BmYQ_AUIBigB

And here's a few pics of the basic frame work. Early days yet, but the shape is there.

[srislash]

Oh yes I see the inlet issue. Should be another fun build though.

[785boats]

Yep. The main thing is the challenge & the fun factor with these boats.

But I've done a few calculations & without ruining the scale features too much, I can increase the inlet areas to about 30% larger than the fan area.The scoops will be a bit larger of course, but the main gain will be by increasing the angle & depth that the concave areas recess into the hull. That makes the area at the rim of the scoop much larger. And then with the extra area of the open cockpit floor added to that, it might just be enough to work. Here's hoping.

[785boats]

Made a bit of progress this afternoon.
Installed the rear blocks to give the stern some strength & the required shape for the skins.
Then the bottom half of the side skins were attached.
The 1/16" ply that I normally skin a hydroplane with, would not conform to the compound curves of this boat, so I decided to use the age old method of balsa planking. That's actually what is shown on the drawings in the smaller scale, with 1/8" balsa.
I used 5mm balsa.
The top will be covered with 5mm x 10mm planks. They will need to be tapered & beveled to fit the curves.
That's the next part of the project. But I'll have to seal the inside with epoxy resin first.
I might even add a bit of fiberglass tape along the joins where the sides meet the bottom of the boat. Just for insurance against cracking as there was a fair bit of pressure on the curves along those joints.

Rear balsa blocks added to form the shape at the rear of the hull

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Starting the side skins.

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Bottom view.

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Side view.

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[785boats]

I cut some sheets of 5mm balsa into 11mm wide strips. & spent a lot of yesterday merrily planking the hull. It's been a long time since I've built a boat in this fashion. Balsa planks on ply frames with good old PVA exterior wood glue. And pins. Lots of pins.

The cowling was already framed up in the hull, so when the glue had set, I cut through the planks at the bulkdead/cowl lines and pried the cowl loose. As I suspected some glue had seeped into the gap between the bulkheads & the cowl frames so it took a fair amount of persuading to get the cowl free. a few chips & dings to patch up, but that's easy.

So now I need to cut the holes for the air intakes & the cockpit. Hopefully the cowl won't spring out of shape with 3 big holes in it.

The final few planks pinned into place.

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The cowl lines cut through

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Cowl off. Plenty of room in there for batteries & ESC etc.

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[Shooter]

That is a true masterpiece.

[785boats]

Thanks Pete.
Not quite yet, but I'll try to do the old boat justice.
Here's something a bit different. The original boat had the rudder mounted on the heel of the front ski.
I wonder how the model will behave with that setup?
It will be interesting to say the least.

[srislash]

Thanks Pete.
Not quite yet, but I'll try to do the old boat justice.
Here's sometjing a bit different. The original.boat had the rudder mounted on the heel of the front ski.
I wonder how the model will behave with that setup?
It will be interesting to say the least.
Oh man, I would be dying to try that, but then I'm peculiar that way. I would not think it would take much travel for it to do its job, for its given purpose. You will likely be playing with the Tx adjustments to get it right.

[785boats]

I too was thinking that it may be sensitive to the controls.
But I did read somewhere that they increased the size of the rudder because he couldn't turn the boat around at the end of a run without assistance.
But if it was on the full size boat, then it's going to be on a scale model too. That's the law isn't it? :biggrin:

Also on my list of world record holders to build, is the Miss Britain III. She also had a rudder at the front of the boat. In front of the main step even. I don't particularly like the look of this boat. But I have to build it at some stage, because I have the plans, and it was such an innovative design for 1933. Here's a couple of pics.

The forward rudder.

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The rudder linkage across the deck.149900

A sketch of the whole boat. It was designed & built in just 10 weeks.

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[785boats]

I hacked into the hull last night and cut out the recessed inlets and lined the resulting hole with some 0.4mm aircraft ply. Looks pretty cool. As stated previously, I made them slightly bigger and deeper into the hull where the rim of the external scoop will be. That created a larger intake area in total.
I shaped a foam block to make the scoops from fiberglass to get a more scale like shape for the final product. A bent piece of ply just won't make the right shape.

The cutouts with the 0.4mm ply added to the hull section.

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A view into the EDF location.

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The cowl removed.

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The foam plug for the air scoops.

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[785boats]

Slowly getting a bit more done.
The scoops have been made.
I made the front Ski today.
A bit of 1/16" ply for the sides. Some foam block for the main shape & some 1/16"ply for the bottom skin.
The heel of the ski was laminated from 2 pieces of 1/8" ply because the rudder post will need to be attached to that part of the ski.
The original boat had a flat Ski, but I added a bit of dihedral into the last part of the ski to try and eliminate the bounce that canards can get with a flat ski.

I also received the pilot that will become John Cobb.
Amazing detail. Almost the same pose as the last photo of John Cobb before his fateful run.

One of the scoops.
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The sides with the foam infill.
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Bottom skin fitted, showing the added dihedral.
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The pilot John Cobb.
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The last photo of Cobb.
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[785boats]

A bit more progress during the week.The bottom halves of the sponsons were made from some 1/16" ply & epoxied to the spars.
As it was St Patrick's day, a few pints of Guinness seemed appropriate at the time.
I also glassed the main hull. Another coat of resin & then the cowls & headrest can be attached.

The basic sponsons.
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Epoxied to the spars.
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Bottom skins added.
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The three forward panels epoxied together. A few pints of Guinness to celebrate St Patrick's Day.
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Glass-work on the main hull ready for trimming.
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[Beaux]

Very cool.

[785boats]

Thanks Beaux.

[boredom.is.me]

Back at it again!

[785boats]

Yeah.
I get bits & pieces done now & then. It's all about time.

[785boats]

A report on the last few days/evenings.
Firstly. I added some carbon fiber tubes to the spars & into the main hull, for some added strength.
Then I trimmed the top edges of the sponsons with some 5mm sq balsa & then filled them with 2 part foam.
Next the balsa blocks were cut, epoxied on to the sponsons, & then carved & sanded to shape.

The inlet cowls & headrest were epoxied on to the hull, & then the whole thing was given a coat of finishing resin. That's the second coat for the main hull, but the first for the sponsons. They will need sanding & a second coat applied.
Now the fun begins. I have to strip the EDF out of the Spirit of Australia & set it up in this boat so I can make up the thrust tube.

Carbon tubes added for strength.
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Two part foam added.
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Balsa blocks added & shaped.
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Inlet cowls & headrest added.
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A closeup view.
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[fweasel]

Its really taking shape now. Your build threads make it look so easy. :beerchug:

[785boats]

Thanks.
Some is easy. Some is difficult. Some is just tedious. But it's all fun.
But yes it's starting to look like the real thing.
The last thing to do now for the hull, is the shrouds around the main spars. More balsa blocks methinks.This falls into the tedious category.

[785boats]

The fan & thrust tube have now been set up in this boat.
All I need to do now is fashion up some mounts. That's tomorrow evenings work.

I also made up a platform in the cockpit for the pilot to sit on, while leaving as much open space around it for more air inlet area. I had to cut some off the bottom of the figure to get him low enough.

EDF, thrust tube, ESC & batteries, all fitted.
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The batteries slide in under the EDF.
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Captain Cobb in the office.
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[Tamelesstgr]

The batteries slide in under the EDF.
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This looks so bada$$

[Beaux]

Luv the driver or pilot.

[785boats]

Kenny.
They do look menacing, don't they.

Beaux.
Some amazing detail on those pilots.

[785boats]

I spent most of the weekend watching the coverage of the Formula 1 event here in Australia, but I managed to get a bit more done on the Crusader in between practices, qualifying, support races & the main race.

The first thing was the mounts for the EDF. Just some 1/2" wood for the main bearers, & some ply gussets to spread the load to the stringers, bulkhead, & the side of the hull.

Then it was on to boxing in the spars with some 12mm balsa & epoxy.
I carved & sanded the leading edges to shape & stuck them on first. Then the top & bottom blocks were added. And finally the rear blocks were shaped & epoxied on
There's a few gaps to fill. But hey. There's nothing a pound of putty won't fix.:biggrin:

EDF mounts & ply gussets.
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Ply doublers on the front bulkhead.
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Boxing in the main spars. Just the trailing edge blocks to epoxy on.
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Just some final sanding & filling to do now.
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[785boats]

Finally got all the filling & sanding & coats of spray putty & sanding done.
So today (Easter Good Friday holiday) I sprayed a coat of base primer on it & sanded that all back.
Then I gave the cowling a coat of silver to see if it looked about the right shade. It'll do me.
I'll get a coat on the hull tomorrow if the weather stays fine.

[srislash]

Man that is looking good!!

[grsboats]

Great buildings like yours previous ones...Congrats Gill

[785boats]

Thanks guys.
It's coming together nicely now.
I've put a hold on the painting & decided to set up the rudder & servo, so I don't damage the finish paintwork by doing it later.
I had to make up a small stuffing tube, & a bracket & spacer to bolt it on to the heel of the ski. I also butchered an old rudder & added a 4mm shaft into it.
Here's a funny thing that almost caught me out when setting up the servo & linkages.. Because the rudder is at the front of the boat it has to swing the opposite way compared to a rudder on the transom to achieve the same direction direction of turn.
I know it can be changed with the tx but I run about 30 boats off the one TX unit & I like to keep all the functions the same to avoid confusion.

The rudder & 4mm shaft.
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Stuffing tube, bracket & spacer.
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Inside the boat. Just needs the brackets for the servo, & a brace across the tube to the sides of the boat.
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[golfito]

Great!!!

[785boats]

Over the last couple of days I've masked off the red trim colour & sprayed it on.
So here she is Almost ready for a test run.

[bob horowitz]

That is fabulous. You are a master!
Bob

[fweasel]

What a monster of a boat.

[golfito]

Awesome!

[785boats]

Thanks for the compliments guys. I'm happy with the way this one turned out.
Here are some stats.

Scale...1/8
Length... 1170mm ( 46" )
Finished hull weight c/w servo & rudder...2660g ( 5lb 14oz )
9s 6000mah ( 3 x 3s )...1394g
ESC & UBEC ...280g
90mm EDF...600g
Rx...6g
Pilot...25g

Total...4965g ( 10lb 15oz )

Pretty light for this Whale of a boat. I hope she gets up on the plane as easily as the Spirit of Australia did.

[Beaux]

That is one cool boat, good luck.

[785boats]

Thanks for that Beaux.

[golfito]

I wait to see it in operation!
Regards!
Hernán.

[785boats]

Well she had her first test run today.
A dismal failure I'm afraid. It just wouldn't get up onto the plane. Just ploughed through the water. Those front struts pushing a wave of water in front of them.
After discussions with fellow club members, it was decided that the reason is that the drive line of the thrust is a bit too negative & just wants to push the nose down. Added to that, the CoG is too far forward for a canard set up. I knew it probably was, but I can't move the packs any further back. I'll sort something out .
Either by raising the rear of the thrust tube or adding a horizontal stabiliser into the rear of the tube to deflect the thrust upwards & push the rear of the boat down a bit. Or both.
The GoG is my main concern though.
Might even need a bigger fan .

[785boats]

I've had no time to work on this boat until last Sunday
So, I hacked into it & ripped out the fan & mounts so I could move the fan further back in the boat 8 inches to the rear bulkhead.
I also dropped it down to reduce the negative angle of the thrust line. It's now a tad positive which should push the rear down & help raise the nose instead of pushing it down into the water.
That only moved the COG back 1-1/2 inches from the original position. I don't think that will be enough. I might need to add weight to the rear. We will see at the next test. It all depends on what effect the change in the thrust line has.
The rudder may still be a problem, as it had no turning effect at slow speed.

Original position.

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New position. 8" further back & lower down to change the thrust line from negative to positive.

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[golfito]

What a beautiful challenge !.

[785boats]

Yes golfito. A beautiful old boat. And certainly a challenge.

[785boats]

Well the challenge beat me I'm sorry to say.
The last lot of changes didn't help at all. After a few attempts I just couldn't get it up on the plane. The front struts just plowed through the water & the poor thing wouldn't get up above a fast walking pace.
I finally bit the bullet & decided to take out the fan & put in a normal motor & drive system.

I got started on it a couple of days ago. Finally.
So, out came the fan, ESC, servo & front rudder. And the thrust tube.
The only strut I had that was long enough to reach the bottom of the sponsons from the transom was an old 1/4" one that was 100mm long. I only wanted to run a 3/16 drive line so I put a sleeve in it & a 3/16" floating bush.
The stuffing tube then needed a couple of pieces of tube added to the end of it to fit snugly into the front of the strut.
I knocked up a motor mount from some aluminium angle & that was epoxied & glassed into the hull along with the stuffing tube.

I had a 160mm long rudder but no bracket for it. So, one had to be made.
There should be enough rudder in the water for straight line runs.
So then a 1/8" aluminium transom doubler was cut & epoxied to the inside of the transom.
The strut & rudder bracket were drilled & tapped on to the transom.
A servo rod was fashioned up & installed through to the engine bay. A servo bracket was made up & fitted beside the motor.

The cog is a lot further back, now that I can fit the packs all the way to the back of the boat.
Hopefully it is enough.

The ESC I use for the EDF is a Flycolor HV 150A. It has no water cooling which is fine when it is in the airway of the fan.
But I needed to add a couple of cooling tubes to the finned cooling plate, now that it will need to be water cooled. I had to bend the fins first to allow the brass tube to fit in between them, & then with a liberal application of thermal adhesive the tubes were pressed into place. It should be fine for the short straightline runs the boat will be doing.

I've just got to block up all the air intakes & the exhaust now, & she will be ready for another test.

The strut setup.
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Rudder & strut.
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Motor & servo mounts installed. Also Epoxy putty around the stuffing tube for added strength.
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The 2 x 4s packs easily fit right to the back of the boat now.
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The cooling tubes added to the Flycolor HV 150A ESC.
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[fweasel]

Knowing what you know now, if you could go back, would you just have left it as it was after the first few test runs on the fan? Or, was that just never good enough and this major revision was inevitable?

[785boats]

After running a few canards I knew that the cog was too far forward. I expressed my concerns in Post #1 & had already accepted that it may need to be converted to a surface drive. I was hopeful that the previous relocation of the fan might be enough. But it was not to be. The cog was still too far forward.
I did contemplate adding about 1/2" of balsa on the front ski to raise the angle of attack. But I didn't think it would raise those front struts out of the water to allow it to pick up speed.
Adding weight at the very rear might have helped.
A larger fan was considered, but would have been inefficient because the exhaust opening of the thrust tube can't be made any bigger. It was only just big enough for a 90mm fan.
So I bit the bullet & changed the fan for the surface drive.

But trust me. The next one I build will be the Hustler, and that one will work with an EDF as it is similar to the Spirit of Australia but with no air intake restrictions.

https://www.youtube.com/watch?v=h_jTL4hL0Bo

[golfito]

Following your work, you are a great builder.
I like the idea of the EDF!

[Beaux]

looks like that ought to work. Good job.

[785boats]

Thanks golfito, Beaux.

I just dug theses two pic out of my files.
The first one at rest, shows that the struts don't actually touch the water. Not even out where they attach to the sponsons. That's how my boat sat in the water.
The second pic shows the boat moving off at slow speed. See how the water is being pushed by the struts & how it flows over the struts & on the sponsons. That's exactly what happened with my model. The EDF just couldn't push the boat through it, & allow the front ski to lift up onto the plane with more speed.
Curious how both the full size boat & the model have that problem with the struts, when they aren't touching the water at rest. I can't understand it.

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How it should have been running.
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[Jesse J]

I think there are two compounding effects.
The first is shared with the full scale: the bow wake lines up with the front strut and only hits it when underway at a specific early speed.
The second is that the edf doesn't have the thrust until it can have a sufficient amount of air moving through it.
The combination at that early speed is maximum drag and minimum thrust...
Solution, maybe a solid rocket booster?

[ray schrauwen]

I think there are two compounding effects.
The first is shared with the full scale: the bow wake lines up with the front strut and only hits it when underway at a specific early speed.
The second is that the edf doesn't have the thrust until it can have a sufficient amount of air moving through it.
The combination at that early speed is maximum drag and minimum thrust...
Solution, maybe a solid rocket booster?

Yeah BABY!! :flashfire:

[785boats]

Totally correct on both counts Jesse.
But another thing I have realised too, is that, at the slow speed the water also rides up the sides of the sponsons & over the top of them, completely burying them with a fair weight of water. This would also contribute to the hull not being able to lift up on to the plane.

[Jesse J]

Spray rails?

[785boats]

Yes. I thought of that as I typed the last post. Pity I didn't notice it in that photo before I took the fan out. I would have tried it. I didn't really recognise it on the model until I saw it in the photo & realised what it was doing. But the cog would still have been too far forward, I feel.
Should get a few test runs in tomorrow, I hope.
The spray rails might still be needed. We shall see.

[785boats]

I had a few successful runs with the Crusader today.
It was only at our smaller track at Boondal, not at our full race track, so I couldn't get it up to full speed. But it looks promising.
The first runs (not in either of the videos) were a bit bouncy when it was at high speed, so I added a tad of negative angle to the strut. Still couldn't use full throttle but it was much better at higher speed.
Prop was an x447/3 motor is an HET 4083 1080kv on 8s. I might drop it back to 6s, because I think it will be too far above scale speed when I open it right up.
Here's a couple of short videos posted on my channel. I'm happy with the way it performed. Even though it wasn't with an EDF.

https://www.youtube.com/channel/UCmckFCp5vHpw83p9Hn-l1hg

[zooma]

Way better than the leaf blower power.

[785boats]

Unfortunately, yes.

[golfito]

I loved it. Beautiful model
I found a model recently that left me impressed:155915

[785boats]

Thanks man.
Yes. I've really got to put some effort in, & finish mine off.

https://forums.offshoreelectrics.com/showthread.php?10145-K7-Bluebird&highlight=bluebird

[golfito]

Subscribed to the thread!

[Jesse J]

I had a few successful runs with the Crusader today.
It was only at our smaller track at Boondal, not at our full race track, so I couldn't get it up to full speed. But it looks promising.
The first runs (not in either of the videos) were a bit bouncy when it was at high speed, so I added a tad of negative angle to the strut. Still couldn't use full throttle but it was much better at higher speed.
Prop was an x447/3 motor is an HET 4083 1080kv on 8s. I might drop it back to 6s, because I think it will be too far above scale speed when I open it right up.
Here's a couple of short videos posted on my channel. I'm happy with the way it performed. Even though it wasn't with an EDF.

https://www.youtube.com/channel/UCmckFCp5vHpw83p9Hn-l1hg
Looks real nice, even navigating the Lilly pads!

[785boats]

Thanks.
I got caught in the lilies a couple of times, & had to go out & get it.

[785boats]

A better video.
A bit short but it shows what she is capable of.


https://www.youtube.com/watch?v=n4aOfjHmvcY

[srislash]

Nice Pail. That is all power.

[785boats]

Thanks mate.
Looks like she needs a fraction more negative angle in the strut to stop the bouncing of the front sponson into the wind.
The full size one started doing that just before it disintegrated, with tragic results.


https://www.youtube.com/watch?v=aYrafKbTqV4

[srislash]

Wow, that actually pulled the nose in.

Yeah I meant all power because the prop on the model seems to be holding the nose up. A bit of neg should do it