MFA Spearfish unfinished kit

[Mike Turner 1Participant @miketurner1]

Hi,

I am totally new to r/c boating. I have just inherited an unfinished MFA Spearfish kit that has been sitting in a loft for 35 years. It is just the hull/superstructure/propshaft/rudder plus a couple of other bits. No instructions!

I am quite handy so will just make it up as I go along. I have been doing some research on motors etc and would appreciate feedback as to whether I am on the right track.

In terms of motor I was looking at the Mtroniks G2 Hydra 30 1100KV from Howes. Battery LiPo 2200mAh 3S. Is the battery sufficient capacity or would I need 5000mAh or bigger?

What is the best way to fit the superstructure to the hull? Both are fibreglass. Should it be fibreglassed or silicone so it could be prised apart in case of major refit?

Thanks for any assistance.

Mike

[Mike Turner 1Participant @miketurner1]

[harry smith 1Participant @harrysmith1]

Hi Mike

The 1100KV would be disappointing on 2S.

My mate is running a 35mm 1450KV on 4S 5800mah with a 120Amp ESC and a 40mm 2Blade prop.

It's dam fast, but handles like on rails.

Is the boat a Mark 1 or 2 ???

The Mark 2 had a lift off cabin with the stern floor.

The Mark 1 had a lift out stern floor only.

Canabus

[Dave Cooper 6Participant @davecooper6]

Hi Mike

Welcome to the forum.

I was just thinking that after 35 years 'up aloft', all might not be well in the leaks department. May be an idea to pop it into the bath /garden pond /children's paddling pool etc and see if it floats….

It would be a pity to do a lot of other work and then find you have more fundamental problems to solve first.

All being well, I'm sure the others will be able to advise you on motors, ESC's batteries and superstructure (I'm not really qualified here).

Happy modelling,

Dave C

[ashley needhamParticipant @ashleyneedham69188]

I glued the top and bottom of my Fantome together with marine grade silicone sealer. This NOT the same as bath sealer, it is much tougher….however, a decent quality silicone should be ok, and it will allow some movement between top and bottom, considering the size of the thing and presumably the lack of internal bulkheads (mine has none).

Harrys suggestion has merit but probably a 3s is enough for any sane person…

Ashley

[Mike Turner 1Participant @miketurner1]

Hi everyone, Thanks for the insights.

The Spearfish is a Mark 1. I will look into the slightly larger (1450 KV) motor. The MFA 850 brushed motor has been suggested but I would prefer the brushless option.

Am I correct in assuming to get all the running gear/radio etc sorted in the hull before glueing the two together. There is a small loose triangle of plywood that I assume is a fillet to go between the prop shaft and the bottom of the hull. Is there any value in trying to decrease the angle of the prop shaft at all? Currently approx 15˚.

Thanks again for all the useful comments.

Mike

[ashley needhamParticipant @ashleyneedham69188]

Mike. The 850 was what MFA sold to go in the boat, and that will give a reasonable performance. I have an MFA Seahawk of similar size which was run with an 850 and the 12v gell battery (as i had one) as per MFA instructions and it was ok. It obviously went better with a 10 cell nimh and would have gone even better on a 3s.

Consider the 850 puts out about 120 watts or so, then you will have an appreciation of the power needed to go quite fast, although twice the power does not mean twice the speed. Current consumption also plays a part…ie how long a run time do you want from your battery,

The Seahawk was re engined a while ago with a watercooled 540 sized inrunner, spec unknown from something i scrapped but i think about 2600kv and the boat goes the best ever even on just a 7.2 nimh ! And flies along on 9.6v. This is relative of course, our pond is not that big, and the boat is well fast enough for it, however on Harry's big open waters it would likely be only adequate.

Ashley

[harry smith 1Participant @harrysmith1]

HI Mike

http://www.youtube.com/watch?v=hPyyUq_eLS0

The Spearfish on 4S, 1450kv .

It's at the end on the video.

Enjoy

Harry

[ashley needhamParticipant @ashleyneedham69188]

Fast, very.

Ashley

[Mike Turner 1Participant @miketurner1]

Harry & Ashley, Thanks for the advice & inspiration. Will definitely try and follow Harry's recommendations on power unit. Seems a bit of a world shortage on 1450KV's but no hurray at the moment. I will probably post more Q's as I proceed. If I want to share progress & pics should I do it within this thread or start another project related one?

Checked up Fairey website and the actual original has a 15˚ propshaft angle.

Mike

[Kev.WParticipant @kev-w]

Mike, if you're struggling to get a 1450kv motor, you could always try a 1500kv instead.

They are on sale at a VERY reduced price here … Graupner motor

[ashley needhamParticipant @ashleyneedham69188]

Mike. The angle of the dangle is a hotly debated subject here. If the shaft is ok and is fixed in securely I would not touch it.

Like the Graupner motor..a bargain, you should buy one right away.

Ashley

[Mike Turner 1Participant @miketurner1]

Kev, Thanks for the heads up on motor!

Model is just a bare hull and superstructure at the moment. Prop shaft and prop are in the box. Thanks to all the supportive advice I feel a lot more confident to press ahead.

Mike

[harry smith 1Participant @harrysmith1]

Hi Mike

The longer the case on the motor the more power it puts out!!!!

The 1450kv we use is 48mm long.

Power output is 1600Watts on 6S, but less on 4S .

Still gets the boat to 40KPHour which is fast.

I did try it on 6S but the boat would not handle it .

Harry

[Paul StillmanParticipant @paulstillman85687]

Hello, re using the Graupner motor – where can i get a mount from please? Thanks

[ashley needhamParticipant @ashleyneedham69188]

Paul. Welcome to the forum.

Make your own mount. Screw the allow cross mount to the motor and drill holes in a bit of 6mm ply to suit the outer holes (use the alloy cross as a template).use 3mm ( i think that’s the size but check) nyloc nuts and bolts to secure to the ply, and glue the now shaped ply in the boat to suit.

Ashley

[Trevor Drabble 1Participant @trevordrabble1]

Paul , The alloy cross iin the second picture is the motor mount . Trevor.

[ashley needhamParticipant @ashleyneedham69188]

Sort of yes and no. The alloy bit spreads the load and ensures the motor sits on something flat, however the motor can be screwed directly to a bit of wood or another alloy sheet.

personally i use the alloy cross and screw this to the motor and then the cross to the bearer, but others here at Bushy dont, they just screw the motor to the bulkhead (OR whatever).

i think Paul is referring to an `L` shaped bracket or some such.?

Ashley

[Paul StillmanParticipant @paulstillman85687]

Hello, thank you for the mount help. Next hurdle is a coupler for brushless motor please? The Grauphner comes with a thread, washer and nut which looks like 6mm. Thanks again.

[Paul StillmanParticipant @paulstillman85687]

Pls ignore last post. I just use the 4mm shaft the other end right? Doh!

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