MM337

[cheddar24manParticipant @cheddar24man]

Just received the plans for my new build, the famous MM337 Thorneycroft MTB Model Boat.

Looking ahead, what would be the optimum power/drive system for this. I presume a brushed motor would be the way to go for slow speed when required.

Twin screws via a gearbox?

[Richard SimpsonParticipant @richardsimpson88330]

There are many views on a twin screw set up, some prefer the simplicity of a single motor and gearbox, some prefer the flexibility and manoeuvrability you can get with independent motors separately controlled.  No right or wrong way of doing it, just do what you prefer.

[Colin BishopModerator @colinbishop34627]

That is quite a big model at 36 inches (900mm) in length. To get best performance you might want to opt for brushless motors and LiPo batteries. Not sure about slow speed but you are unlikely to be doing that much of the that most of the time and the latest brushless controllers are reputed to give decent low speed handling.

The torque of the brushless motors should not require a gearbox.

Colin

[cheddar24manParticipant @cheddar24man]

Thanks folks. I’ve got several brushless motors with ESCs and LiPos so will experiment once built. The other consideration is prop size, matching it to the motor. Lot to think about.

[cheddar24manParticipant @cheddar24man]

It’s been years since I looked at a plan and am definitely in need of a bit of help Understanding them.

One sheet has a side and the top layout, see photo, but I can’t work out where the deck edges are or the side panel outlines are, for cutting purposes.

Maybe come a bit clearer once I have built the framework?

[cheddar24manParticipant @cheddar24man]

Umm, seem †o have a bit of an issue now that the keel is in place with its location in the #1 bulkhead?

The bow reinforcing plates are as per drawing but they have lifted the keel up at the #1 bulkhead which will make chamfering quite a challenge?

Think I might have to unglue the front end (UGH!) and then cut the bottoms off the reinforcing pads to lower the keel further into the #1 bulkhead? All other bulkheads/keel location look ok to allow chamfering.

[Colin BishopModerator @colinbishop34627]

What about the top of #1 bulkhead – is that at the same deck level as the others?

Colin

[John W EParticipant @johnwe]

hi there

Couple of things – looking at the plan it is actually built as a box section hull.  So, you have 2 side pieces which Vic calls the crutches.   All your frames when assembled into the crutches, should sit level at the top of the crutches or in other words deck level.  So, if this is the case, the frames are correct.  Therefore, you may have made a small error with the height of the keel, as this should sit into frame B1 near enough perfectly.

The other thing I can see is the Thorneycroft MTB 73 ft version was powered by 4 motors geared through gearboxes to drive 2 shafts.   This information may be amended if and when I find out more  on this particular vessel.

John

 

 

 

 

[Richard SimpsonParticipant @richardsimpson88330]

Are you building from scratch from the plans or are you using the Belair Kits parts set of pre-cut ply parts?

[cheddar24manParticipant @cheddar24man]

I cheated and got the Belair kit of ply parts.

I have discovered that the keel notch in #2 bulkhead is not as deep as on the drawing causing the keel to “rock” at this point and to lift it at the bow.

I have now increased the depth of this notch and the keel site perfectly all along!! Tut tut Belair!

[Richard SimpsonParticipant @richardsimpson88330]

That makes sense.  I don’t think its cheating, I’m a great one for making life as easy as possible and not taking on big time consuming jobs that you are not going to enjoy doing!

[cheddar24manParticipant @cheddar24man]

Thanks Richard.

I have now increased the depth of the keel location in #2 bulkhead and the keel sits right down into the #1 bulkhead location – much better!

Thank goodness I haven’t fully glued the keel in place!!

[cheddar24manParticipant @cheddar24man]

Basic question I’m sure but I did warn you!

Does one do the keel and bow section chamfering after putting the side planking on or before? I’d believe before so that the planking meets at the bottom of the keel making a “point”.

[Richard SimpsonParticipant @richardsimpson88330]

The chamfering is to help the planking sit on a flat surface rather than sit on a sharp edge, so giving a better edge to glue as well as preventing creases in the surface of the hull.

[Ray Wood 3Participant @raywood3]

Hi Cheddar,

Many of these plywood kits of parts are scanned from the drawings by folk who haven’t a clue about building a model boat !! and the parts don’t fit  Shame really 🙁 they were hand drawn back in the day not CAD !!

People make a right meal out of my Wild Duck design all the time with the kit of ply parts from SARIK !!

Regards ray

[cheddar24manParticipant @cheddar24man]

Agree Ray, the laser cut parts don’t go together very well without quite a lot of modification which is a shame at £70+!

I have however now got the almost completed framework with a level deck front to back. I find that the deck actually has a slight curve port to starboard! (I hope, mine does!)

Thanks Richard for confirming my thoughts. Now to spread the dust🤣

[John W EParticipant @johnwe]

Hi ya there Cheddar

Two things – first one, 99% of ships, vessels, boats have what is called camber on the deck – or – a slight radius, curve.   This is to facilitate the water to run off the deck when water is on the deck.  We replicate this on a lot of our models; which Vic has done on these drawings.   Here is a scan of Frame B1 from the original Vic Smeed drawings.

The second things is about chamfering your ribs / frames at the edge; this is, as  Richard has said, to facilitate the smooth run of planks.

To help you get it right; we generally use a nice flat and square edged piece of wood – long enough to cover 3 or 4 frames which is laid across the edge of the frames.   This will give you an idea of how much you need to sand off.   Again, I will put a pic on to show you what is meant.

Admittedly, this is of a tug build, but, it is the same principle.

I believe you have asked questions regarding the skinning of this vessel on another Forum.  i.e. bending the plywood and soaking it.    If you use thin enough ply such as 1/16th thick ply.   It should conform to the bends quite easily.    Or, have you thought about diagonally planking the hull?

John

[cheddar24manParticipant @cheddar24man]

Thanks John, all taken on board!

Couple more examples for the incorrect laser cutting. The stringers just don’t fit correctly, will have to do some serious sanding to bring them flush with the bulkheads and B6 doesn’t sit correctly, about ⅛” above the deck level!

[cheddar24manParticipant @cheddar24man]

Now begins the sanding, unfortunately no easy way to do it!

I must admit I have little idea how to go about planking the sides, whether to use two full length panels each side or vertical planking?

[Colin BishopModerator @colinbishop34627]

There is no reason why you cannot use both methods. For the flat sides of the hull use single sheets and where the compound curves develop at the bow then use vertical strips of an appropriate width. If adopting this approach then 3mm medium balsa might be the best material as you can smooth off the transition from the sheet to the strips without leaving obvious break lines. Then seal and protect the hull with resin impregnated lightweight glass cloth which also helps bind everything together.

Up at the bow where the curves are tight, it is common practice to insert balsa blocks and carve them  to shape. The objective is to produce an overall smooth hull and there is no reason not to use different methods in combination. I do it all the time.

Colin

[cheddar24manParticipant @cheddar24man]

Um, thought I’d replied?

Many thanks Colin. I’ve got some 0.8mm ply so will have a go at full length panels. If that fails I’ll go the balsa route. I’ll keep the thread posted.

[James Hill 5Participant @jameshill5]

Hi Cheddar.

That’s a nice looking hull. It’ll make into a nice model.

Regarding planking, it’s not as difficult as it might seem. I’d never done anything like it before I built my Surfury, and I double diagonal planked that. On the current Puffer build, Iv’e done what others have, a mixture of sheet where it helps , and then planked other parts.

Best of luck with your build,

Jim.

[cheddar24manParticipant @cheddar24man]

Planking the sides…………

[Colin BishopModerator @colinbishop34627]

It is important to have a sharp edge at the chine where the upper and lower hull sheets meet as this helps prevent water ‘climbing’ the hull and assists speed and performance.

Colin

[cheddar24manParticipant @cheddar24man]

Thanks again Colin.

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