British Hovercraft: Saunders-Roe, BHC, Griffon, Vosper, Vickers etc...

[Rick Lowe]

There is also a twin-gun turret hiding at the rear...

[PR19_Kit]

As they have turrets both fore and aft, what are they using the rest of that VAST hull for?

And just thinking about firing a hefty gun from a hovercraft, with almost no friction between the 'craft and the surface, the recoil will have a hefty effect on the track and the speed of the 'craft surely?

[Weaver]

There is also a twin-gun turret hiding at the rear...

Indeed - you can't see much of it, but judging by the barrel length, I'd guess it to be a twin 30 or 35mm, of which there were a number of options in this timeframe. The spacing of the guns and the little bit of wedge-shaped turret that's visible might suggest that it's an Emerlec twin 30mm. Alternatively, it might be an Oerlikon/OTO twin 35mm (same gun pods as the Gepard SPAAG). Whatever it is, I'd have put another one on the front.

Emerlec 30mm:


Oerlikon/OTO GDM-C 35mm (aft gun - couldn't find a better pic: they didn't sell many):




Another couple of issues with the 76mm (all assuming that it's supposed to be an OTO-Melara 76/62 Compact: the drawing's a little 'loose'):

1. It weighs 7.5 tons empty and that's all right at the front,

2. There doesn't look to be enough room underneath it for the standard ammo feed mechanism, and OTO-Melara only recently came up with a low-profile above-deck mount for this gun.

[jcf]

........ see my post #52................

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Yikes: that 76mm has got a LOT of recoil for a lightweight structure to absorb. I'd have been more inclined to fit twin 40 or 35mm at each end and depend on rate-of-fire to compensate for the aiming difficulties.

The structure is not as lightweight as you seem to think, they're not an aircraft style monococque.
All of the SARO/BHC machines start with the bouyancy tank, basically a strong raft built using standard boat-building techniques, everything else is attached to that raft. The superstructure is mounted to that base but does not contribute to the strength of the whole, it's a glorified deckhouse. The frames, bulkheads, longerons etc. of the cabin structure support some equipment and define the shape of the superstructure. The external skins attach to the frames etc.. The buoyancy tank of the SR.N4 was heavily built because of its intended role as a car ferry. Reinforcing the tank to take the weight and recoil of the gun wouldn't be difficult. As to the damage to Princess Margaret in 1985 after hitting the breakwater, a conventional boat would also have been heavily damaged, depending on type, the damage could have been far worse with the vessel sinking quickly rather than staying afloat, which reduced casualties. The damage to Princess Anne while attempting the Calais to Dover run in heavy weather was limited to the superstructure at the stbd. bow, it did not effect the strength of the bouyancy tank or render the craft inoperable.
You need to bear in mind that the Saunders company started as a boat-builder and had built all-metal flying boats and amphibians, which required robust structure, decades before they ever built a hovercraft. 

[jcf]

Technically not British but as it's Bell it fits.
😉
Late '70s Bell proposal for a car ferry using the LCAC as a basis.

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[PR19_Kit]

That's a pretty big LCAC, it looks at least twice as large as the USN version, maybe three times.

[jcf]

That's a pretty big LCAC, it looks at least twice as large as the USN version, maybe three times.

Evidently it was supposedly going to use the standard LCAC lift and propulsion engine package, but I'd think that it would require more lift blowers which would eat more horsepower.
🤔
It seems to me that it was one of those typical front office "let's maximize our profit by leveraging
our existing product" deals. The engineers shrug and do it, they're getting paid either way so it's
no skin off their nose. Pointing out the problems is pointless, but as long as you get it on the record you're covered.
😉

[PR19_Kit]

Having at long last got three of Airfix's SRN4 hovercraft, I started some serious work on making one of the lengthened Mk 3 SRN4s. Not quite as 'lengthened' or as 'widened' as TomZ's SRN8, but some of the way there.

It won't be a Whiff as I want to make one as they were when I worked on them in the mid-70s, taking oil samples from the hydraulic system, naturally.

Trying to find accurate drawings etc. turns out to be a nightmare as there just aren't enough distinct dimensions available. For instance, is the length measured with the doors open or closed, and is the width measured outside the skirts when they're inflated, or not?

So I took one of my Airfix kits and taped it up a bit, not an easy task as the sprue gates are the width of the Channel Tunnel, and half the parts don't have the part no. tags on them either. Some of the parts BHC didn't change when they updated the Mk 2s and 3s were the loading doors, and I travelled aboard them in all three versions, and I was pretty sure of that, so I measured the width of the rear door entry and used that as a 'master dimension'.

Scaling the various available drawings proves that a) they're all to DIFFERENT scales, even though presented as one drawing, and b) they're anything BUT consistent! But eventually I managed to come up with a reasonable (I think....) version of the Mk 3 plan to enable me to start chopping plastic, and I'll open a thread on it when things have progressed a bit more.

Here's the Mk 3 drawing with the plastic Mk floor in place above it, showing just how much BHC stretched it!

[Weaver]

Nice one Kit.

I'm still ploughing through a book on Ton-class MCMVs, picking up little snippets about crewing and roles as I go. On the one hand, it's slow work, but it's a little gratifying that much of my initial guesswork seems to have been in the ball park.

[jcf]

Only the cabin width changed, the bouyancy tank (raft/hull/deck) width did not change.
The basic deck width of all marks was the same. The cabin was just a superstructure
mounted on the bouyancy tank, changing its width had no effect on the underlying
bouyancy tank structure.
There's no need to widen the tank/raft/hull/deck, just the cabin. The skirt was enlarged
and widened to support the increased cargo weight, but this didn't effect the bouyancy
tank width.

[PR19_Kit]

I know that, and don't plan to change the hull width.

What's almost impossible is to change the skirt arrangement from Airfix's Mk 1 skirt. The shapes are entirely different, but won't be so noticeable with it un-inflated of course.