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>> Home > Forum > Boat Specific Chit Chat! > EarlyVosper M.T.B by Simplas
EarlyVosper M.T.B by Simplas
(256 views)
Author Message
boaty
(Admiral)





Forum Posts: 55
20th Sep 2018 13:20  
>> Permalink
mdlbt.com/46372

Found on E Bay but sold in June of this year, a 42 inch kit of a Simplas Marine Construction Vosper M.T.B. It would appear that there are not many about now.
I built one in 1972 and the kit contained a fibreglass hull with all fittings including the guns being in cast metal. Deck and superstructure were plywood and the boat was a model of an early Vosper as it had a very narrow beam and torpedo tubes were towards the stern.
I fitted a DC Sabre 1.5cc diesel but had to add a lot of ballast which resulted in a sharp drop in performance. This was solved by replacing the Sabre with a Fuji 15 marine version glowplug engine . The boat was free running and as I was on an apprentice engineers pay and could not afford r.c.as I was having to support an ageing Mini. This was my transport from Ellesmere Port to the boating lake in New Brighton. If I had bought a Taycol Supermarine motor it would have solved all my problems as the battery would have been the ballast.
Boaty
😁


Dave Keech
onetenor
(Fleet Admiral!)





Forum Posts: 400
21st Sep 2018 00:22  
>> Permalink
mdlbt.com/46390

Maybe but ballast ,is ballast,is ballast. However it's achieved. The overall effect is the same. Would the Taycol Supermarine have had more power than the Fuji? Or at least the equivalent.?👍

RNinMunich
(Fleet Admiral!)





Forum Posts: 2305
21st Sep 2018 01:06  
>> Permalink
mdlbt.com/46393

"Maybe but ballast ,is ballast,is ballast. However it's achieved."
Sure John, but at least a heavy battery is useful load and not 'just' ballast.😉
Have no idea what shaft power the Fuji produces (only know their excellent 35mm film😉) but the Taycol Supermarine is rated at 22.5mHP (22.5/1000HP) at 3.5A, 4000rpm. Efficiency 52% 🤔 so you have to stick twice as much electrical power in to achieve that!
Sooo, given that 1HP = 745.7 Watts -
And electrically P=IxV (Current x Volts)
22.5/1000HP = (745.7*22.5)/1000 = 16.778W so ~33.55W in.
Thus if I = 3.5A they must have done that test / measurement at about 9.6V. The Supermarine also runs great at 12V but maybe not with max efficiency!?
With a spec weight of 2&1/2 lb i don't even want to get into Power to Weight Ratio, although I measured Colin's motor at 947gm = 2.0877776229lb 😉
But then, some of the motor had corroded away
As I'm currently renovating a Supermarine for Colin H. This makes me start thinking about rigging up a test jig so I can see what it actually produces!!! Always up for a challenge 😁 Got nowt else to do 😁😁
Would be useful for other motors as well if I can get it figured out😉
Happy fiddlin' folks, cheers, Doug 😎


Attached Files - Click To View Large


Young at heart - slightly older in other places 😉 Cheers Doug
Grant me the Serenity to accept things I can't change, - the Courage to change things that I can,
and the Wisdom to know the difference!
onetenor
(Fleet Admiral!)





Forum Posts: 400
21st Sep 2018 02:35  
>> Permalink
mdlbt.com/46397

Hi Doug Yep you're right about the battery of course. This might help if you can plough through it as the sections are a bit scattered.----http://sceptreflight.net/Model%20Engine%20Tests/Fuji%2015-IV... I haven't read it right through so don't know if there is enough info for comparison.👍 Night all😎

boaty
(Admiral)





Forum Posts: 55
21st Sep 2018 10:48  
>> Permalink
mdlbt.com/46399

Hi Onetenor

Fuji 15 was a good glow engine which I don't think it is manufactured any more. Aero version max B.H.P was just below .40 when tested. If it was in a model aircraft it would have been around .20 to .25 depending on prop size which was good then for a small capacity glowplug . Marine versions when on the water put out a little less and the water cooled jacket was never as efficient as the finned cylinder jacket of the aero version.
My two Aerokits boats, the Sea Commander and the Crash Tender are powered by single Speed 600 motors running on either 8.4 or 9.6 volt Ni Mh batteries. Performance is equal to that of marine diesel power such as the 2.46 Ed Racer and D.C 2.46 Rapier, the latter I used to watch in the fast steering events in the early 1960s at Fleetwood and Coronation Park in Crosby just outside Liverpool. Taycol powered versions would be obviously slower due to the additional weight were far more reliable and you did not have to put up with injuries from excessive use of a starting cord with kids watching and "extracting the urine" shouting "why wont it go mister".

Boaty


Dave Keech
RNinMunich
(Fleet Admiral!)





Forum Posts: 2305
21st Sep 2018 10:53  
>> Permalink
mdlbt.com/46400

Hi John,
Near the bottom of the article peak power of 0.41bhp @ 20500 rpm (!) is mentioned, so almost twenty times the power of the Supermarine at ~ 5 times the revs😲 Cheers, Doug 😎


Attached Files - Click To View Large


Young at heart - slightly older in other places 😉 Cheers Doug
Grant me the Serenity to accept things I can't change, - the Courage to change things that I can,
and the Wisdom to know the difference!