Help with Large Model Boat

[Red Admiral]

I have a large (54 inch) semi displacement model boat. I currently have a Torpedo 850 12v electric motor installed in it which is connected to a 3 Bladed 45mm brass prop. Is there anything that i could do to increase the speed of the boat? Thankyou

[bugfanatic]

Can you post some pics showing detail like hardware, shape of hull, battery, etc.?

[Red Admiral]

Here are some links to pictures of the boat. The battery a 12v Lead Acid. She still looks a bit scruffy becuause I have not yet finished restoring her.

The Hardware (http://www.fairlineturboownersclub.co.uk/hardware.jpg)

Bow (http://www.fairlineturboownersclub.co.uk/bow.jpg)

Stern (http://www.fairlineturboownersclub.co.uk/stern.jpg)

Side View (http://www.fairlineturboownersclub.co.uk/full.jpg)

[Doubledog]

Got just the ticket for you... my zenoah 230 ! :D

23 cc's putting out 2,8 hp! I'll even sell you the clutch so it can come to an idle. Install the stock exhaust and it'll sound good too. :o

Messing around guy, its all in fun. :)

I'm no electrical guru like a few guys here but if it was mine, what would I do? Humm...<scratch head now>

Just don't really know other than changing the battery and running more cells. The more you have, generally the more speed you get.

[bugfanatic]

Yeah, DD is right. You need a motor with more 'oomph'. You can't lighten the boat because you need it to sit right in the water, & only weight will make it sit at the correct water line. That 12v battery has plenty of amps, so you'll need 1 or more motors that can use that juice a little better. The best way would be to go brushless, but there are a lot of good brushed machine-wound modified motors out there with 15 or more turns for some real push. I mean it looks like the motor you have is plenty strong, but what kind of revs do you think it produces? Also, it wouldn't hurt to evaluate the prop. Maybe the motor is fine & you just need more pitch or a larger prop - it does look a little small for that hull. You'll have to see if there is something out there that not only keeps the look of your boat correct, but has the correct size & pitch for your boat. You can make a brick fly with a big enough engine, I think the same holds true for a boat. Since you are pushing more than riding on top of the water, you'll need more muscle to get it to ride with authority. Not sure if I helped much.

[Red Admiral]

How much would an engine like the one you mentioned (zenoah 230) be with all the equipment I would need, also, how much would a suitable brushless motor be?

[Red Admiral]

The motor is supposed to turn at 9778 rpm and have a power output of 157 watts. I have tried 3 different props, the one i have on at the moment makes the boat go the fastest. It says that the motor can go up to 15v, would it make a significant difference if I connected it to a 15v battery? What size of brushless motor would I need for it? They look expensive!!

[Hydro Junkie]

Sound to me like a new motor is needed. As you are only drawing about 13 amps, a higher RPM motor, maybe with a gear drive for more torque, might be called for. This would let you spin a bigger prop with more pitch. Have you considerred running multiple props and motors? That might be an answer too :) Also are you using a speed or power prop? That may also be part of the problem.

Hey Bugfanatic, aren't we supposed to be talking boats, not F-4 Phantoms? After all, they were described as flying bricks :D hehehe

[Red Admiral]

What kind of motor with a gear drive and more torque would you suggest?? If I installed another Torpedo 850 motor would it make is go significantly faster??
I am very grateful for your help, I have only just got into R/C boats and I am not very knowlageable yet!

[bugfanatic]

An F-4 is cool. I remember when I was a kid watching the Blue Angels fly them. Anyway, back to boats.... I think a reducing gear drive with a bigger prop would help a lot, but so would 2 electric motors. That 12v battery could easily power another 850 motor, & then each motor would push half the mass through the water making each a little more efficient. You could gear them both together to spin a larger single prop so you don't have to change the stuffing box etc. & keep the current layout. Brushless is expensive & you'll have to change speed control as well as motor - but the tradeoff is the same power from one brushless motor compared to 2 850's. Another 850 plus another prop would be about your cheapest investment. If you wanted to experiment, you could have someone mod your current prop for more pitch & see if it works a litttle better. I think that even with more pitch though, that prop is still a little small. See what the largest prop is you can fit under there that fits your prop shaft & go from there. I know that larger boats sometimes use Kort nozzles to improve efficiency, you can get those as well as props for this boat from Dumas. A 40mm prop is roughly 1.57", can you fit a 1.75" or 2" prop under there? If so... http://www2.towerhobbies.com/cgi-bin/WTI0095P?FVSEARCH=dumas+prop&FVPROFIL=++

[Red Admiral]

I cannot fit a larger prop to the boat, the 45mm prop that is on at the moment only just misses the bottom of the hull. If I were to fit two motors geared together that were connected to the same prop and shaft would it make it go much faster or would I still need a larger prop or a prop with a larger pitch? I have another 2 bladed prop with a huge pitch on it but when I connect it to the motor it blows the fuse.

[bugfanatic]

No, the same prop won't do much better just by increasing revs, unless you can REALLY increase them. See if someone can tweak the pitch for you. What size is that fuse?

[bugfanatic]

No, the same prop won't do much better just by increasing revs, unless you can REALLY increase them. See if someone can tweak the pitch for you. What size is that fuse?

[Hydro Junkie]

I'm thinking twin drives. I can't see why the person who built the boat left so little room for the prop. I think trying twin drives with counter rotating props might be a viable answer. It would require plugging the present stuffing box and installing two new ones parallel to the kiel, with a brace of some sort at the aft end of each. You might also get power props from Harbor Models or Ships N' Things, as they both specialize in ships and tugboats. I know they both carry props that are both right and left handed just for counter rotation :) Almost forgot, with the twin shafts, you will loose a little of the rudder control. With the prop directly in front of the rudder, the prop forces water into the rudder. With the props out to the sides, the rudder looses this, making the rudder less effective. You may also want to make a larger rudder to compensate for this effect.

[Red Admiral]

The fuse is 15Amp. If I converted her to twin screw, would I still need larger props? I have a local model shop that I can buy all the gear for her. That is where I got all the other bits from. Would it be a good idea to position the props nearer to the rudder if I was to convert her?

[Hydro Junkie]

Moving the props close to the rudder will give you the same problem you have now, lack of room to experiment. I would try about half way between the kiel and the side of the boat. This will give you room to experiment while keeping the props under the boat :)

[Hydro Junkie]

Just was doing some research on props. Found Ships N' Things to carry Raboesch Props. They carry several different styles and blade counts. If you want to stay with the single screw design, all their props at 45mm diameter have a 46.1mm pitch. If you want to go with multiple props, they carry many sizes, some styles to 130mm. At Harbor Models, they carry Rivabo brand props, again in multiple sizes, in three, four and five blade styles. They also carry Prop Shop props in multiple styles and sizes. Just so you know, the Raboesch props are much more expensive than the others.

[Red Admiral]

I have decied to convert her to twin screw, what size props would you reccomend for her?

[bugfanatic]

Twin screws? That sounds great. I'd leave plenty of room under there. You never know if you need something as large as a 2.5" (63.5mm) prop. I doubt you would, but.... you never know. I'm sure a couple screws around 2" should work, depending on pitch.

[bufferoo]

Just a suggestion before you go full bore with a coversion. Can you extend the drive shaft a little? That "may" just give you the clearance that you need with the hull to increase the diameter of the prop. If it doesn't work, at least you were able to find out without any major mods or work to the hull. Should be able to do it in under an hour.

Bufferoo

[Red Admiral]

The only way I can extend the current shaft is to buy a longer one, the one that is in only just sticks out far enough for me to connect the motor to it!!

[Chris LaPanse]

If you do any major speed-increasing mods, get rid of the fuse. 15A is less than what my 30" mono pulls at 20mph. This will be a huge limiting factor if it is in the circuit. Good luck

[Red Admiral]

Thanks Chris, I will put in a larger fuse and give the larger prop a try. Are you sure that dooing this wont burn out the motor?

[Hydro Junkie]

No it won't burn up the motor. As long as you don't overload the motor, it will be fine. If you run the boat and it comes back with a motor too hot to hold, your prop is too big. If the motor comes back cool to cold, you can run more prop.

[Red Admiral]

I have tried a larger fuse and a prop with more pitch and came back to hot to hold, the prop is too large! I am going to convert her to twin screw when I have saved up the money! Thanks for all your help! If I have any more queries I will definatly come back to here!

[blizard05]

[QUOTE=Red Admiral][FONT=Arial]I have a large (54 inch) semi displacement model boat. I currently have a Torpedo 850 12v electric motor installed in it which is connected to a 3 Bladed 45mm brass prop. Is there anything that i could do to increase the speed of the boat? semi disp hulls ar limited in speed by ther design dbl power does not =more speed try using old coardles drill moter

[hemayann]

i heard about your problem im only 14 but, i had a similar problem with my model. my boat is 780mm long and that weight of it is 6 kg a lot to push through the water. i had a standard 40mm plastic prop. i tried to increase the pitch in which i did but i've only got a 1.6mm sharft it worked, also you mite need a powerfuller motor