Thanks guys........now I'll take a month or so to digest all this great info, and post some results in a while.

Hi Mister Bee
Reading brushless motors e.g. 3639-1100kv it's diameter is 36mm and 39mm long. Battery handling 2S to4S(7.4 to 14.8 volts).
Power 8oo watts so required ESC 60 Amps.
What the specs do not say is the water prop size, but, only aircraft prop sizes.
For this size motor a 2 blade 40mm is a good start.
The 1100kv is the revs per volt, so 3S(11.1 volts) 12210 rpm and on 4s(14.8 volts)16280 rpm.
Another couple of motors are the D3548/4-1100kv(910watts),the 3025-1500kv(1300watts) and the 3648-1450kv (1600watts).
These will use the same ESC and Lipo battery(5800mah 40-60C).

THis is the Going brushless article. bit gentle for starters.

www.modelboats.co.uk/news/article/going-brushless/8029

Hi Brian
Not the boat I thought it was. Misread your reference to cockpit as Cabin so was looking at a totally different model.

We had a similar model in the club and it was very well built and weighed a ton. Hopefully your model is not as heavy and does I believe have a planing hull.

What motor was originally fitted? As Derek indicated earlier a motor of similar size to that originally fitted would be a good starting point. I would look for a motor of around 1000Kv and 3/500watts if using an outrunner but inrunners are usually 2000Kv and similar wattage.

Without seeing the model and space available it is difficult to be precise but there a many suppliers on line that give details of motors available that might suit your setup. if you look on the Component Shop website they have some reasonably priced motors and EScs. I suggest you pick a combination that will fit and matches your price range. Higher current motors need more expensive ESCs and higher capacity batteries. You haven't mentioned what batteries you intend to use but NiMhs will work OK. if you really want the speed and sparkling performance then the cost will escalate as you will be considering LiPos which will need a dedicated LiPo charger.

Hopefully you have provided enough info and other members who may have a Chris Craft or similar model will share their setup and experience.
Dave

And another.

Thanks, Dave,
So much info!

This a Dumas kit built in Houston, Texas.

Hope the photos are clear enough,

Brian.

Hi Brian
I am not sure which model you are referring to but your description of period photos suggests it is from the late 1930's and yes they were not a planing hull.
Does your model have one or two props? A few pics of the model would help, you can upload by clicking the yellow box to the left of this input panel.
Brushless can be a bit daunting at first experience but they are not difficult to use once you are familiar.

You will already have seen they have three input wires and these need to be connected to an individual Brushless ESC for each motor. Doesn't matter which wired connect to which socket on the ESC but if your prop spins the wrong way you can swop any two connections to change the directiopn.

The kv rating refers to the unloaded speed of the motor for every volt you apply so for say a 1000kv motor supplied with 11.1volts the motor would spin at 11100 revs.

There are two types of brushless motor "in-runners" and "out-runners". This refers to the construction used with in-runners generally being less bulky. The outrunners will produce more tork and can be more suited to slower speeds. if you need to water cool the in-runners have a jacket fitted around the motor body whilst the out-runners use a water cooled mounting attached to the bearing. Both are suitable but I personally prefer Out-runners. For your model I suspect an inrunner may be preferable due to the restricted space available.

Unlike brushed motors brushless do not like being overloaded and work best when they can achieve their max efficiency at near max revs. They have a max watt rating which should not be exceeded (Watts = Amps x Volts). The casing may be marked with numbers 42-56 which is the diameter 42mm and length 56mm.

In my 48" Sea Queen I use a 42 size 850Kv water cooled motor of 700 watts and it is happy driving a Prop Shop prop of 42mm at 45 amp on full throttle.

To measure your wattage you need to acquire a Wattmeter to measure the actual current draw with the model in the water. This will give an indication of the max current at max load as you hold the model stationery.

If the watts are greater than the motor's rating you need to reduce the prop size/pitch. I like scale props so use 3 bladed brass and avoid using racing plastic/nylon props as they can overload the motor.

The ESC should also be of a sufficient rating to handle the running current, I usually try for at least a 50% margin ie 75amps for a 50amp max current.

Finally your setup must be really secure (I know from personal experience) and free running. The revs produced are possibly higher than what you may have experience before and any fault can and will escalate very quickly. At high currents the motor coils will fry in about 2 seconds should anything stall the motor and you can expect to see smoke and a ruined motor.

If you post some pics we can give you more detailed help on your particular setup.
Dave

HI Derek, sorry to hear about your sight problem, hope it goes well in the near future. The article you mentioned by John Parker, could you email me a copy please? I am like you, short of knowledge on brushless motors

Regards

Mark

There is light hearted article called "Going brush less" by John Parker on the web somewhere. Worth an introduction. I have a copy if you can't find it. ps. if I'm not spelling well I have sight issue at moment.

I'm no expert on this, so will leave to others. But while wait.I also have one with the original silly size prop thread. So let that alone. Mine runs on brushed at about scale with. Was told spray rails on the hull help planing. Regards brushess. if a 1000kv. That means for every battery volt used, it's 1000rpm. So 1000 kV x11.v (lipo) or whatever is used gives motor speed. Personally I'd do what I do,use a similarly size can to the brushed one you have from eBay. A speed control from eBay China . I have some good water proof stupid Amp rating ones. never a moments bother. around £15 I think.
Have fun once you get someone more knowledgeable.