30-40cm carbon fibre hull

[minigazz]

Hi, this is my first post on this brilliant site! Basically I am looking to build a carbon fibre boat hull which is between 30 and 40 cm in length. I want the boat to be fast, reliable and stable - ie i dont want to be fishing it out of the middle of the bond with a big stick because it has turned over! I have previous experience in making boats, including a 60cm wooden catamaran, a 35cm vacuum formed HIPs mono and a modified NQD tear into - all with moderate success.

I also have a little experience in composites, however I do not have the knowhow to make a boat hull and I am very unsure of how you would go about this (ie mould making/joins/canopy etc)

I am very unsure of what type of hull to make too, I know the mono's are considered easier to setup, but I tried a surface drive with my mono hull and it didn't perform very stably at all.

I was hoping to pick you guys brains on my issues here!

Here are some links to my previous projects - enjoy!

http://www.youtube.com/watch?v=oecj6fFaSAA
http://www.youtube.com/watch?v=JtaINgMCkFg
http://www.youtube.com/watch?v=cJSpn-4BwxA

[Cope]

I cant help you with your building as I have yet to try making a hull.

As far as the little yellow mono goes, I would try to make the battery movable for CG changes. This should help keep it from leaping out of the water.

Your builds look nice. Good job.

EDIT- you may also want to check and see if the hull is true on the bottom. If your hull is untrue at those speeds your guaranteed chine walk. At that speed you may even want some hook (A small indention in the ride surface) in the rear. Hopefully someone who knows more than me about designing hulls will chime in and say for sure.

[minigazz]

Ah, thank you! It really does have issues with jumping out the water! I did try moving the battery but it then started submarining! The lipos really did bring that thing to life! I was thinking maybe a carbon fibre version with a little longer hull would act more stably? I also dont like the poor handling due to the surface drive and offset rudder.

[Cope]

See if you can try to get some video of it running on smooth water,It would help folks more. It's hard to tell much when running in a creek.

Your right, Longer will be better.

Looks like the sucker handles great to me?

You can get or make a non off set rudder if that's what you don't like?
Most folks off set the rudder to help with prop walk. I would think at your speed prop walk is a major issue? Are you using sharpened and well balanced props? If not that could be a large issue.

You have a very small boat going at considerable speed, (up current even) everything needs to be just right.

Again very nice job.
:beerchug:.

[minigazz]

Yea, I had kind of tossed it aside as I thought it was overpowered and underdesigned - I will get it going at some point during easter if i can and then get some footage. Am i right in thinking the chine walk is the rocking motion where the bow of the boat jumps up and down? I think I am expecting too much from a surface drive system, I would probably be better with a sub-surface system? Is prop walk where the boat moves sideways or 'strafes'? If so then this wasn't really much of an issue. cheers

[minigazz]

Here is my flickr page if it is of interest http://www.flickr.com/photos/60718745@N06/sets/72157626282078644/

[Cope]

In my first post I edited out where i suggested getting an adjustable strut. It seems all the new boats are going surface drive. You may have good luck with going to a new stuffing tube and an adjustable strut, but I think you can just bend the out drive a little?

Yeah prop walk is the boat tending to turn to the left under power. (For counterclockwise rotating props)
Chine walk is side to side.
porpoising is jumping up and down and is the thing I see in your video.

Have you tried many other props? that one may just not be right for the boat?

You could also just go to JAE or zipkits and get some free plans for a nice rough water mono and scale them to your size? With your building skills it should be a walk in the park?

[minigazz]

Thanks, i will be sure to check them sites out!

If that is porposing then I have labeled that video wrongly :-s oops!

I want something fast like that one, but much easier to drive! As i mentioned I have a modified NQD tear into which is quite fast, but nothing too special and a little plasticy as it is basically a kids toy with brushless power!

Sadly that boat uses a shaft rather than a wire, so bending it isn't really a possibility!

Thanks for your help - its the first time I have ever used a forum before, it would have made my past project much easier!

[SweetAccord]

If I had your skills to build a boat I would not try to re-invent the wheel. I would just get a bare hull or copy one as there are many great hull designs out there already. If you want speed a rigger are excellent in speed and handling.

Just my stupid opinion.

[Cope]

Why not go to a flex shaft drive? wont last as long but will allow some fine tuning.

[minigazz]

Yea, I like building things from scratch though! I will look into flex drive shafts - they seem very expensive here in the uk though!

[sundog]

Minigazz, one problem with the yellow boat is you are using an outrunner motor in a narrow hull. That's why it is corkscrewing (barrelroll). Go to an inrunner motor - a 20x40mm size and keep the speed below 3000kv. That should give you good response and speed.

[minigazz]

Well I ran the other day with an inrunner motor and it seemed a little more controlled if nothing else! I didnt get any footage unfortunately as my only camera is my iPhone and I didnt fancy juggling it with this thing while trying to keep it under control!

What I found was that it would jump out of the water very frequently, giving poor control and not allowing you to really open it up. I moved the battery as far forward as possible, but it ended up just submarining, which caused water to get in and ruin my lovely £5.50 ESC - sadface!

I dont understand how the flexishafts work and what parts i need to implement one into my boat. My understanding is that you have a strut on the transom which holds a solid shaft with some bearings or bushes in and the flexishaft connects to this somehow? I dont understand how the shaft tube connects to this though and how leaking is prevented at the transom.

Cheers!

[Cope]

The flex fits into the stuffing tube, this fit along with grease and the direction of the winds in the flex keep water out. The flex is held to the motor with a collet or grub/set screw coupler. the end of the flex can go to another coupler that holds the threaded drive shaft or just be a welded flex where the drive shaft and flex are welded together.

See here. (EDIT-Scroll down ;) )

http://www.offshoreelectrics.com/categories.php?cat=17

[minigazz]

Thanks! I was looking at using a similar size motor for this hull (ebay special mystery 1000-5000kv on 3s), would this be sufficient or should i be looking bigger? also, how do these motors compare to a quality motor of similar size/weight like a hacker?

cheers

[sundog]

Well I ran the other day with an inrunner motor and it seemed a little more controlled if nothing else! I didnt get any footage unfortunately as my only camera is my iPhone and I didnt fancy juggling it with this thing while trying to keep it under control!

What I found was that it would jump out of the water very frequently, giving poor control and not allowing you to really open it up. I moved the battery as far forward as possible, but it ended up just submarining, which caused water to get in and ruin my lovely £5.50 ESC - sadface!

I dont understand how the flexishafts work and what parts i need to implement one into my boat. My understanding is that you have a strut on the transom which holds a solid shaft with some bearings or bushes in and the flexishaft connects to this somehow? I dont understand how the shaft tube connects to this though and how leaking is prevented at the transom.

Cheers!

I think the problem is with the stuffing tube (strut) being so long, and exiting the hull so low in the transom that when the boat planes and gets up on the bottom blade of the prop, the boat is completely out of the water at that point. If you were to have the shaft exit the hull higher on the transom, it would settle down at speed. But finding that exact location might be elusive. That's where a strut comes in.

[minigazz]

I think you may be right there! I have tried shortening the stuffing tube and have tried to reduce the angle between the shaft and the bottom plane of the hull. I have also experimented with a wire drive. It still wont settle though! It porpoises terribly and flips over sometimes. Could it be the hull design or is it still workable?

[minigazz]

Also, with a flex shaft, does the flex shaft have to be held in a tube all the way from the motor/shaft coupling to the stringer drive?

[sundog]

Also, with a flex shaft, does the flex shaft have to be held in a tube all the way from the motor/shaft coupling to the stringer drive?

That is customary. But you could try just moving the shaft up in the transom to get the hull to come down some. In other words, drill another hole above where it is now and try it again. Can you take a picture of the side of the boat showing the transom and prop shaft. From that I can give you a good idea of where to drill the hole. Try to get a level, flat shot from the side. (see crappy drawing)

[minigazz]

I dont have access to a camera right now, however it is currently as low as it will possibly go (approx 1.5mm of the very bottom of the hull). I also noticed that the motor and speedo got very hot today, and the speedo strated playing up (its only a cheepy one off ebay from hong kong), but the props i use are about as small as i can get hold of for a 4mm threaded shaft and the motor is only 3000kv @ 11.1v?

[minigazz]

I am now in a position to start the design work on my new hull as I finally have some free time! I am pretty sure I am going to go for a mono and given the high price of carbon fibre I think I am going to use fibreglass initially.

When it comes to moulding the hull I assume i am going to have to make the hull in two parts - an upper and a lower part. I do not however want this join to be visible from the outside of the hull - this means no lips around the edge. I don't know if this is possible though to get a good enough join?

I also have no idea whether to go for a plug/mould constructed using balsa/ply planking over a ribbed frame of just to carve the hull plug from a solid piece of wood, i.e. mahogany?

Finally (for now, lol) I was wondering if anyone could recommend me a power setup for a fibreglass hull of approx 40cm in length. In the past I have used ebay motors and very cheap ebay escs (which seem to work well for around 15mins then die!)

Thanks

[aahwhatever2]

:popcorn2:

[minigazz]

Hi, would anyone know if it is worth me adding steps to hull this design? I have decided on a length of 38cm as it seems a good compromise between portability and stability. If it is worth doing, are there any rules to follow? Im hoping to finish the plans for the plug tomorrow so i can start the exciting stuff!

[minigazz]

I have now started my build blog here http://forums.offshoreelectrics.com/showthread.php?26679-New-Scratch-built-fibreglass-carbon-mono-build