Power Boat Surfury

[William WillsParticipant @williamwills84452]

I am in the spraying stage for this hull. It was built from drgs sent to me by Renato Levi many years ago. I will post some pics when I have finished the paint work.

I would appreciate help in selecting a motor (brushless?) to provide a scale speed (It is not intended for racing!) I cannot seem to find data on revs, prop sizes, for marine use of brushless motors – it all seems to be high revs and large airscrew data. I really would appreciate any help this way.

[William WillsParticipant @williamwills84452]

21 1/2 inch hull

[William WillsParticipant @williamwills84452]

Sorry everyone the hull length is 27 1/2 inches! My mistake – apologies.

[John W EParticipant @johnwe]

hi there

I also built the Surfury a while ago, I used the Myhobbystore plans. Although the plans are a bit vague there was an article in the Model Boats magazine, I think its a 1969 issue – or circa ….where the hull is diagonally planked and soforth. In my model I fitted an I.C. engine and that was an Enya 19 model – it was purely built for nostalgia that model. I have tested my model in a test tank i.e. a rather large paddling pool – and basically that is as far as it got. The model still needs finishing off. The thing is with these models, and which you will already realise – with the hull being a steep V shape, they are brilliant in going in straight lines, but, when you try and turn them they are a nightmare. As far as powering it with brushless, I will be honest with you, I don't have a clue, because brushless is still a new field to me – along with lipo batteries & etc.

Couple of pics of my attempt

[harry smith 1Participant @harrysmith1]

Hi William

At our model boat club a large number of members use a 35mm 750kv brushless motor with a 2 blade 40mm prop.

These are models about 28 to 36 inches and would give you a bit more than scale speed.

The motor is a Hobbyking 3639-750kv 600watts, on 2S(7.4 volts)Lipo battery 5550 rpm, on 3S(11.1 volts)8325 rpm).

If you use a 60 Amp ESC which handles 2-4S batteries you can up the speed by changing batteries or use the sister motor the 3639-1100kv.

As for battery capacity 4000mah to 5800mah with a C rating of 40, a low voltage alarm is required(part number Voltage-Alarm).

The black one, this checks total voltage and each cell voltage.

[William WillsParticipant @williamwills84452]

Harry. Many thanks for a very detailed and informative reply – just what was needed! I will lookup the data on all of the suggested motors, batteries etc. It will while away the hours while the paint is drying. I had the great pleasure of seeing Surfury perform in the 1969/71 era and also photographing it in detail when under refurbishment in the Groves & Guttridge yard here in Cowes. I would be pleased to supply anyone with copies if required for detailing purposes. Again, many thanks. sincerely, Bill Wills

[harry smith 1Participant @harrysmith1]

Hi William

Had a look on u tube about the Surfury(the real one) what a beast!!!

I would skip the 3639-750 and go the 3639-1100, also get a 3S and a 4S battery.

I installed a 3639-1100 in my off shore ABS racer, started with the 3S battery and upgraded to the 4S with the same 40mm prop.

I got a bit bored with it, so I installed a 3648-1450 kv 1600 watt using the same prop, ESC and started with the 3S battery for rough water and the 4S for calm water.

I tested it with the 4S in rough water and it was a bit insane!!!

It handled to water OK but the wind was the problem, one gust of wind I stood it up at about 70 degrees.

I cannot move the battery forward to move the balance point forward which would fix the problem.

Harry

[William WillsParticipant @williamwills84452]

Thanks Harry, invaluable data. Your final runs in rough water and resulting attitude of the craft in the wind was a real life situation. I have many photos of many of the Cowes/Torquay runners just you describe. Let me know if you would like any Surfury shots. Right forward in the nose were two ballast tanks. I have the nose clear in the model and could fit any solid ballast before sealing. Regards, Bill

[harry smith 1Participant @harrysmith1]

Hi Bill

The trouble with sealing solid ballast in you have no way of adding to or removing.

A plastic or metal long can with a screw top glued into the bow would give you away of adding to or removing.

Add a bit of foam to stop the lead moving.

The battery position makes a big difference.

I was luckily with Sea Hornet, I used a 3S 2650mah battery behind the rear seat and only had to add a small bit of weight under the front seat.

I added to much weight to start with and the boat bow dug in on turning.

Harry

[John W EParticipant @johnwe]

Hi there William

I received your emails and sorry for the delay in responding,

When I originally built the model of The Surfury there seemed to be a lot more information and drawings available on the web. The one drawing I was looking for, and I have been trying to research is where there is a cutaway view of the Surfury which shows the position of her fuel tanks and if my memory serves me well, the 2 main fuel tanks are mounted either side of her twin engines (on the Surfury the 2 engines were in line driving fore and aft through a central V gearbox).

I am sure I remember reading that the main purpose of the ballast tanks, at the bow of the boat, were used to compensate the usage of fuel – as the boat progressed in the race (as the fuel is used the centre of gravity moves in the boat) and to bring it back to the central position for optimum performance, they would either pump water into the tanks or remove water, whichever was the case. Also to assist with the trim of the boat there are powered trimtabs on the stern which would be adjusted accordingly to bring the bow down.

my personal opinion, is that it is the worst thing to do to add weight to a performance model. My recommendation would be to dispense with the weight in the bow and move the batteries as far forward as is possible towards the bow and ensure that you incorporate adjustable trimtabs at the stern of the model and this way you will be able to trim the model to run the model at the correct trim and also keep the model as light as possible to get a greater performance.

and what do I know I am just a bluebird duck

john

[harry smith 1Participant @harrysmith1]

Hi Chaps

The battery is the best weight you can use.

A bit off set to correct prop torque, install the motor as forward as you can and as low as you can.

I test run my Sea Commander today with a 50 gram heaver battery and the performance was a bit better with the bow sitting a little lower at full speed, but, the turning circle decreased a bit more at speed so I had to watch it in the turns.

I do not think a cabin cruiser pulls 40 mph and sits up like a speedboat!!

[William WillsParticipant @williamwills84452]

Dear Harry, sorry for the delay as I have been away. I take your point about using the battery as ballast and can quite easily accommodate this. Many thanks for your invaluable help. Regards Bill

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