Ferry Motor Requirement

Hi,
I am currently designing a small ferry that will help the transportation system in the 3rd world regions of Cambodia. It is a simple 4 x 6m ferry that has a duel hull. (ie a catamaran) It will be built out of bamboo for the platform, and Coakee wood for the hulls. It will carry up to 25 people and tow 4 small canoes. I estimated the weight at about 2 tonne for the boat and will tow about 1 tonne too.
However i am struggling to figure out how much power and what kind of motor I would need to move the boat at about 15-20km/hr.

If anyone had any ideas could you please let me know?? And any other ideas would be welcome.

Thanks alot

 

For that load and speed up to 20kph you would ideally go to length of about 8m to get easy powering. Looking at something like 20HP outboard or say 15HP diesel with a bigger prop than the outboard.

Of course it depend on the 1 tonne that it is towing. If it is lead the boat will not go very fast at all. Would be better to carry it on the main hull. If it is long and slender the speed will drop by say 20% when towing.

You will need something more substantial to tie the hulls together than bamboo. The bamboo could be used for a deck over bearers but would not have the structural integrity to tie the hulls together unless arranged in a complex engineered structure.

Rick W

 

Thanks Rick,

Yeah it will will have to have a strong wooden frame connecting the two hulls, thanks for that. It will be towing peoples own personal canoes so they can still get around after departing the ferry.
Do you mind asking what kind of experience you have? I am not doubting your knowledge at all, its just that i need to reference my sources for this project.
Thanks mate

 

I currently design and build high efficiency boats - best performance for limited power. Mostly aimed for human power to get the most from least effort. I usually work with lightweight composite materials.

I am an electrical engineer but have been around a long time in industry and managed multi-discipline engineering teams. Boating is a hobby and something I hope to pursue with more time in retirement. Have always been involved with boating for recreation.

Here are some examples:
http://www.boatdesign.net/gallery/showphoto.php/photo/15138/size/big/cat//ppuser/18624
http://www.boatdesign.net/gallery/showphoto.php/photo/14410/size/big/cat//ppuser/18624

http://www.youtube.com/watch?v=OXSZLt_6eFg

http://www.boatdesign.net/forums/at...581d1225663272-pedal-powered-boats-jn_150.wmv

Rick W

 

Wow! that is very impressive, i love the yellow pedal powered one . I am a 3rd year mechanical engineering student.
I was just wondering, with Diesel engine, where should that be mounted on the boat? and what size prop do u reccomend?
Thanks for all the help.

 

A common mounting arrangement in SE Asian craft is the longtail set up like this:
http://www.youtube.com/watch?v=zfvhhReIdHM&feature=related

It is a matter of making a strong gimbaling mounting that is nicely balanced. It gives the advantage of keeping the motor toward the stern while having a shallow shaft angle.

You see some ridiculously large motors set up like this:
http://www.youtube.com/watch?v=1MHkDVo8MPU&feature=related

There must be manufacturers of the long tail but it is not something I have looked at. Frosty might know. Here are some more:
http://www.boatdesign.net/forums/at...1124375875-10m-thai-long-tail-chalongbay1.jpg

Normally the largest diameter prop you can fit will give the best efficiency. It takes a bit of effort to work out the best for the job.

Rick W

 

Ok,
Is a gimbaling mounting where the motor is mounted quite high? and why does this give you the advantage of keepin the motor at the stern??
Thanks

 

The gimbal allows the motor to be tilted and rotated. The shaft is extended out the stern a long way - hence longtail. To get the shallow shaft angle within the length of the catamaran, using a single motor, would require the motor to be set on the deck at the bow. This would cause the boat to sit bow down when not loaded - less than ideal. Having the motor at the stern means it will sit bow up when unloaded. This is much more desirable from a handling point of view.

Normally inboard powered cats have a central faired pod under the deck for the motor or a motor in each hull. These would make construction more complex.

Rick W

 

hamo

Your requirements are a bit vague. The 25 poeple in the 6x4m is that in the 6x4m as in total total deck area? Hence, are the 'hulls' under this deck 6x4 deck-area, or is the 6x4 length and beam of the entire boat? How are you seating them..wooden fix seats running athwartships? Will you be providing a head?
You say 2 tonne for the hulls, is that total or each hull..what about a deckhouse/superstructure, to stop the 25 pass getting wet, has that been included? Will you be providing any lifesaving eqpt (which is always sadly lacking in 3rd countries).
What range, this will dictate your fuel capacity.
Is it for rivers, or inshore water or..??..this shall dictate the hull and its structure.

Just a thought..

 

Ad Hoc,

Sorry about the vague requirements, early stages!
Yes the toatal deck area will be 3x8m (changed) hence the hulls will be under this deck.

The seats will be simple 'bench' seats in rows perpendicular to the hulls.

It will run on a flat lake in a very warm climate, and lifesaving equipment hasn't been considered, but since they live on the lake it will most likley not be necessary. (cost aswell)

The range has not yet been decided as we havn't found the best route yet, but an estimate of 100km.

Thanks