View Full Version : Hull reinforcement

Nickinoue - n/a
9-Jul-07, 09:44 PM

Finished A levels so im back on the hover.

I have been growing concerned for the lack of reinforcement on the hulls deck. With me and the engine im worried it might crack when it hovers?

The deck is 6mm marine ply.

Do you think that adding cross bars of 21mm square pine underneath the hull where the engine is would be a good idea?



jon_curtis - n/a
9-Jul-07, 10:11 PM
dont put bits of wood under the hull, use the engine frame as the floor support, and weld cross bars out of box or angle the width of the hull.

or embed the wood in the inside, with glass and mount the engine on the top of that.

either way, yes it would be a good idea to have support pretty much as you have shown, behind the seat. on the inside tho!

kevinf - n/a
10-Jul-07, 06:54 PM
It won't crack when it hovers - don't forget you have 10-12 lb/ft2 pushing up against the floor when you are on cushion. When I built a Challenger in ply I just reinforced the engine mount positions with aluminium plates on the underside bonded on with a polyurethane adhesive like Sikaflex or similar. Each plate was about 100mm x 150mm.

The bigger problem will be because of the skids when at rest - there will be a 21mm gap under the hull and when you step in or kneel on the floor, the floor will bend and stress. On our craft we use wider (100mm) strips of 10mm ply for skids and put two intermediate skids under the cockpit to reduce the gap that the floor is spanning.


profqwerty - n/a
12-Jul-07, 12:08 AM
For the eagle 1 It was just a piece of 6mm ply. When on the ground it was usually on grass so it didn't flex much. On water it flexed a bit but nothing too bad.

As long as the top of the engine frame is secured properly, the engine shouldn't bend the floor too much. 6mm ply is strong stuff and can bend a significant amount.

With them going across on the bottom, stones etc will eventually start pulling them off.

Nickinoue - n/a
12-Jul-07, 10:59 PM

Now i can see why you wouldnt do what i preposed...i dont want things hitting pine struts at right angles.

I think im going to extend my engine mount sideways from the frame and then mount it to the hull. I think putting aluminium sheet to spread the load is also a good idea.

Do you think that It might be worth hard mounting the frame to the top of the duct, so it cant flex. Jon i remember you saying it might be a good idea...better than using those flexible cotton bobins.


peterd51 - n/a
13-Jul-07, 07:08 AM

the guy that built his hovercraft in the attic, mentioned a few messages back with links, has a site where he details the whole

job from start to finish...

he set up he engine, fan, duct, etc, on a rig that can be lifted in/out of the hovercraft in one 'lump'.

The link for the 'engines' page is: http://www.xs4all.nl/~wcasten/hoverholic/steel/steel%20page (http://www.xs4all.nl/~wcasten/hoverholic/steel/steel%20page.htm). htm

This looks like it could spread the weight over several points.



Nickinoue - n/a
13-Jul-07, 10:00 AM
Cheers peter.

I have designed my frame so it can be removed from the top side pritty quicly, just as you said. I think i got a clear idea now of what to do with the frame.

Cheers all!

jon_curtis - n/a
13-Jul-07, 02:39 PM
hi nick

i would extend the engine frame if it was me, with what you have done so far, its the easiest option. i wouldn't have a huge sheet of ally to spread the load tho! i would just have 75/100mm squares either side of the ply where you bolt thru!

with you frame setup in the pic, i would not have rubber mounts at the top. bolt thru the duct and spread the load in the back of the bellmoutth with a short bit alu bar with a hole in, lying in the curve. you want the duct to stay where it is really http://hovercraft.org.uk/images/icons/smiley_icons/icon_smile.gif

the fan and duct postion will be held together.

your engine is on mounts, are you going to use a flexi coupling to take up the engine movement on the mounts regards to the bottom pulley?

Nickinoue - n/a
14-Jul-07, 10:38 AM

Yehr i think most stuff is sorted now. I do have a flexible coupling between the engine and bottom pully. Once thing that im still unsure is wheather i should have those diagonal supports to hold the frame perfectly at right angles and to stop movement when pressure is applied to the frame when the fan is blowing. I see not alot of people do it, and to be honest its heavy and is really in the way of my air filters, hence the kink half way down where ive bent it to fit.

Would it be better to fit struts from the top of the frame and attach them to the hull as shown in the picure below?

Is it really essential i keep that frame at right angles, i only have a small weld surface holidng the horisontal to the vertical and so i thourght the diagonal supports would be needed?

jon_curtis - n/a
16-Jul-07, 06:18 PM
got any pics of the frame from the side, showing all of it?

Nickinoue - n/a
16-Jul-07, 09:32 PM

profqwerty - n/a
17-Jul-07, 04:22 PM
Good pic - really clears up several of my questions!

I would keep the diagonal braces in to at least guarantee it won't bend forward. On my old hover the back of the duct started to pull away from the hull (helped by my bro crashing it). I put in a couple of diagonal braces and it never had a problem again, although I actually put them between the top of the fan frame and the edge of the cockpit (helps sideways movement i guess!).