Hi Harry,

I agree - the Turnigy 3648-1450KV is indeed a beast of a motor, but I am not sure if it would be best suited to the Sprite Plus that I am building at the moment.

The Swordsman 37 that will hopefully be my next project however would be a perfect hull to fit it into, so I have "reserved" it for that boat.

I have some Surpass "in-runner" motors that I bought some years ago when there was an offer on them. I am using one of them in my Sea Commander at the moment, but I bought them in three different types, so I will check to see what I think may be the best size for the Sprite Plus.

Following a check, the three different sizes that I have are:-

3675 -1580KV.
3675 -1900KV.
3675- 2250KV.

All three motors look identical to each other, and if the optional cooling jackets are slid over the outer casings the specification stamp of the motor is completely hidden.

The 3675-2250KV should certainly have some serious "oomph" - even though in-runner motors have less torque than out-runner motors.

The first picture shows the 3675 motor - ready-mounted so it can be easily slipped between the carbon fibre "side spats" when needed for use in the Sprite Plus

The second picture shows the Surpass motor loosely positioned above the Turnigy 3648-1450KV where the size of these two motors can be easily seen for comparison.

Bob.

Hi Zooma
The 3548-1450 is a beast of a motor and are not made any more.
I am using the Surpass Hobby 3542-1450 kv which is rated at 1050 Watts on 4S.
I have one in the Sea Rover but only on 3S and a 42 mm 2 blade prop.
I have a pair of 3542-1250 kv in my Pro Boat PT 109 on 2S because on 3S it was too dam fast .
The props 3blade 37mm.
Harry
🚤

Hi Harry,

The motor shown is the one that I took out of my restored LesRo Rapier - because it was too fast (and fuel hungry) for use on our local club lake in Southport, and only gave me an average of 8 minutes duration per run.

I run this motor with a 2C LiPo battery pack. I tested it with a 3C LiPo battery and its performance was very similar, but is duration was even less - even after testing with slightly smaller propellers to suite the increased revs etc.

The advantage of the water-cooled motor mounts that I always use is that they allow any motor to be fitted or changed very quickly.

The Turnigy 3648-1450 is a superb motor, but it just happened to be fitted in an engine mount that I picked up for use when making and aligning the motor mounting plate for this Sprite Plus.

I don't know what motor I will be using in this boat yet - other than that it will be brushless (!), but it could be an in-runner as I have had one on my bench for several years that is well overdue to be put to work!

Bob.

Hi Zooma

That motor on 4S Lipo with a 40/42mm 2 blade the Sprite will fly !!!
I have the same motor in my Spearfish/Spear and Swordsman.

The Two Part Engine Bed.

A mock-up was made to check the way that a two part engine bed could be made into an integrated unit when it was combined with the bulkhead that crossed the engine bay.

We had recently scrapped a large model warehouse that we had been using for some years when we used to run a truck club for Wedico radio control trucks, and this was made from 3/8" plywood.

This wood was about 8.5mm thick (in new money) and since the engine mounting plate was to be split into two parts, I thought that it would be a good idea to recycle some of this plywood to make a really sturdy engine plate on which to fix the engine mount.

Using the underside of the bulkhead templates as a guide, the front and rear halves of the motor plates were cut and shaped from this 8.5mm plywood that was used for the base and the ends, with 4mm plywood sides.

The smaller front half of the motor mounting plate was fitted tightly under the motor mount and bonded into place with J.Perkins Rapid bond PVA.

A new solid coupling was quickly machined on the ML10 as the one that I bought with the matching Powerflex coupling was a sloppy fit and I wanted the motor to be held firmly in exactly the correct position while the first of the engine mounting parts was bonded in place.

After this tight fitting solid coupling was fitted, there was zero movement of the engine and its mount and so the first half of the base was held firmly in place underneath it while a small pair of clamps held it against the bulkhead to keep everything aligned until the glue dried.

Bob.

Sprite Plus - fitting the motor mounting baseplate.

With a brushless motor fitted onto the alloy water-cooled mount and joined to the 5mm prop shaft with a solid coupling, the angle of the motor mount assembly can be clearly seen.

The carbon fibre "side spats" of the water cooled motor mount can be seen to be resting nicely on top of the bulkhead cross member.

As luck would have it, the motor mounting "side spats" sit exactly on top of the bulkhead where is crosses through the middle of the engine bay giving the assembly good support in exactly the right place !

The first picture shows the front of the motor mount sitting nicely on top of the bulkhead. (Frame number 4).

The second picture shows the rear of the motor mount on the other side of Frame number 4..

The third picture shows the position that the motor will have to be mounted - partly in-front and partly behind Frame number 4.

This will necessitate the need to have one part of the motor mounting platform in-front of this bulkhead and the other half behind the bulkhead.

Bob.

Sprite Plus.

Having had a rest over Christmas and New Year from building the Sprite Plus prototype, I thought I would take care of the next step - making and fitting an engine mounting plate.

Once this simple job is finished, the adjustable water-cooled alloy motor mount can be fitted to it before the side skins are cut and fitted.

Having fitted the solid 5mm x 5mm coupling to a brushless motor and then screwing this assembly in-between the carbon "side spats" of the motor mount, I had the precise location for the motor to be fitted after it is clamped onto the end of the 5mm prop shaft.

At this stage, I came across a problem that I have not encountered before in all of my 60 or so years of building and restoring Classic Model Power Boats.

The motor has to be mounted on top of a bulkhead that passes directly across the middle of the engine bay. Usually the engine bay is "open" and free of any bulkheads crossing it to give an "uncluttered" and "open" space to plan and fit any type of motor in the best location.

Although the bulkhead that is fitted across the engine bay has a full cut-out, the base of it still has to be "straddled" by the engine mounting plate.

The combination of the shallow angle of the prop shaft and the position of this bulkhead means that the engine mounting plate will have to be made in two halves - one half in-front of this bulkhead, and the other half behind the bulkhead!

The height of the bulkhead cut-out is only just high enough for the motor mounting sides to rest on.

The 6mm motor mounting plate cannot sit on it as it will be too high, so this bulkhead cross member will also become an integrated part of the engine bed (or engine mounting plate).

The motor plate (or engine bed) has to be "rock solid" in any Classic Model Power Boat so this has given me an interesting problem to resolve.

I could cut away 6mm from the shallow base of the bulkhead to make way for the engine mounting plate, but that would weaken the hull (the bulkhead is not very deep at this point any case) and so I have decided not to do that.

As I work my way through this, I will take some pictures to illustrate the problem as I think my words alone cannot describe the situation well enough.

The enclosed picture shows the shape of the bulkhead that runs across the engine compartment (Former number 4).

Bob.

Hi Ronald,

I just use the closest Former (bulkhead) template to give me the correct shape to cut out at each end of the boat stand and allow for the thickness of the bottom skins.

In the case of the Sprite Plus, the ends of the stand locate part-way between Formers, so I averaged the bottom line (that will fit against the skin) between the Formers that are in front and behind the ends and it worked out perfectly.

A cut-out to clear the prop shaft at the desired location was added so that the hull sits really neatly on the stand.

Once the foam pipe insulation is added to each end of the boat stand it does remove the need to be quite so accurate with the cut shapes - but it is nice to know that mine fit well with the boat in the chosen position on the stand before the foams are added.

Bob.

CAD drawing makes the job so much easier and no eraser ✏️ and pencil marks.

I am in the process of "knocking-up" a basic (very basic) stand to put the Sprite Plus on, because when I am working on it (now that it has the bottom skins fitted) - I cannot hold the hull by its keel in the vice any longer!

My "boat stands" look just like the little wooden orange boxes that used to be seen in the green grocers years ago (anyone remember them?) - except those were probably made out of better wood than I use !

I always use scrap wood to make my boat stands from, which may seem a little bit strange to those that spend hours designing and crafting beautifully elegant stands to sit and display their model boats on (some can be works of art in themselves).

My boat basic boat stands are more likely to get a gravel rash from the car park than to be used to display an elegant model boat - but they are very practical and work well enough in the workshop(shed) or beside the lake when they can also be handy for carrying some basic oddments in that may be needed.

Anyway, I am splitting a length of rough-cut square timber to make a pair of sides for the stand, and some plywood has been gained from our r/c model truck club when the garage unit that had been used to practice reversing manoeuvres in etc became surplus to requirements!

Once the stand is put together I can start to make the parts for a good solid engine mount and get a motor and coupling fitted.

Bob.