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[John W E]

This may help you out Steven .


Model Boats Plan Vosper MTB by Glynn Guest & Magazine June 2011 Vol.61 Issue 727 | eBay


John

[Tug Fanatic]

It is an interesting idea to use a rigid coupling and then remove the top bearing of the propshaft to substantially reduce alignment issues.

[Circlip]

 Why not 360s and make it triple screw?    Can never understand the need for speed in a scale or semi scale model? If it was scaled up to full size, would the equivalent speed be possible? Can't remember ANY of the full size MTBs or ASRLs being able to turn on a tanner. Orses for corses.


  Regards  Ian.

[GG]

Tug Fanatic,
           The idea of a rigid coupling sans top tube bearing did work out OK.  It does however remove one barrier to water entering the model but this is not a problem with the proper set up at the bottom end of the prop tube.


Glynn Guest

[John W E]

The build article for the MTB basically follows what Glynn had written in the magazine.  The only time that I differ from what is written in the article is the 'off the shelf' coupling I use and also the motor mount that is also shop bought.  The motor now is mounted upside down using plywood supports plus also location of the battery.  The battery in Glynn's article is mounted across the hull.   I made a battery box that runs the length of the hull in line with the keel.


John

[Steven.T]

Hoping someone here can help...
I've followed the plan to assemble the keel, I cut the keel inline with the drawings to have room for the prop tube at the right angle etc, added the doublers etc. Everything lined up against the drawing when I was building it. However the 228mm prop tube I've ordered seems way too short, if I push it up far enough to get a hold on the coupling, with the bearing just about poking out of the keel top, then the shaft isn't long enough at the other end and the propeller will foul against the keel, it seems about 20mm short from the drawings. Have I done something wrong here or do I just need a longer prop?
Only other thing I can think that would fix it is to cut a fair chunk out of the keel and doublers so the coupling sits futher into the keel, but not sure if this is right.
Thanks
Steven


PXL_20210803_202831070.MP by Steven Trotter, on Flickr

PXL_20210803_202550833.MP by Steven Trotter, on Flickr

PXL_20210803_203314780.MP by Steven Trotter, on Flickr

[TheLongBuild]

Personally I really would not take the plan too literally and do what you think is best, just move the prop away from the keel by 1-2mm by angling it higher at the motor side, or as you say get a longer shaft.

[John W E]

Hi ya Steven


Three questions   are you following instructions of the book


or - the article on here?


1.   The shaft length that you mention seem to correspond to the same shaft length that I used.


2.   What type of coupling are you using?


3.   How are you going to mount the motor?


If you are following Glynn Guest's build, you are going to require a longer prop shaft and a solid coupling.


If you are following the build I did, you will need to cut part of the keel away further and part of the bottom support to accommodate the coupling I used.  Also, you will need to mount the motor upside down which I did - because of the space you will require.


Here is a picture for you.

[Steven.T]

Thanks John,
I'm sort of referencing both the magazine and your write up, but mainly yours.
I'm sure the shaft in the magazine is the same length too, 228mm. But the drawing says 267mm which seems like it would fit on mine.
 I'm using the same coupling as yourself, a flexible one. I was planning on mounting the motor upside down like yours although mine is brushless and possibly shorter.
Looking at it I think either cutting away like you had to would work, or a longer prop would work. I guess the longer prop would be less damaging now it's mostly assembled.
Cheers
Steven