bpyhullgen silver bullet 4.8

Dejay said:

Intuitively, as a totally uneducated opinion, you could probably cut them down to 5cm at least above the waterline. I mean how could anything move after you welded it all together?
You could also cut out large sections on the top and turn them into plexiglass windows to save a bit of weight / stability.
Also if the water is cold it's probably more worthwhile to insulate the bottom half for camping on the water. The water must act as a giant heat sink.

Any thoughts on how much HP / kW motor power you'll have?

Click to expand...

Reducing the ribs above the waterline is a great idea.
To be honest I'll probably just borrow my friends ~80lb (about 1kW) trawling motor to start with.
I had thought about an outboard motor or something like that with but the way the interior space is enclosed I don't really want gas fumes in there. I could have had a separate compartment with a blower but for this build keep it simple.

I have seen some commercially available trawling motors that are 160lb thrust they say equivalent to about 7hp - this could be interesting.

I don't have any speed requirement and haven't done any analysis on drag or power required. Based on 1.35 x waterline length calculation the "hull speed" should be a bit over 5kt.

For starting I'll take it to a lake with no current on a calm wind day and try with my friends trawling motor... If I can leisurely navigate a mile or two and camp on the water the objective is complete.

Revisiting this before going on a river with any sort of current or longer journeys will be necessary.

According to hullcalc.xls you should be able to get going a 5 knots with 674 watts. Which is probably a bit optimistic but doesn't sound too bad. I would have thought the weight would make a bigger difference.

I've never heard of hullcalc.xls - do you have a link or reference to where I can learn more about hullcalc.xls?

http://www.users.on.net/~malcolmandjane/HullCalc/HullCalc.xls

I really have no clue how accurate it is. Better way would be to export an obj and waterline offset for prelimina.com

I few updates from earlier this year... I have been in a different location and not able to work on the project recently. When the build started it was easy to roll over with two people but as the build progressed it became heavier. I ended up building a gantry to turn the boat over and maneuver it. I thought about attaching the hoist to the ceiling but didn't want to stress the wooden building structure. It worked quite well. The top beam is bolted on so it can be dissembled and moved if needed. I may repurpose the gantry as a kids swing or climbing thing outside when not being used - It shouldn't rust.

I've been drafting a design for a trailer. I would like the boat to be able to sit directly on the ground when being used as a camper so it's more stable and safer - lower to the ground. I have tried trailer-able sailboats for camping on land - they work great but the trailer adds a lot of height and when you are up on the top it's a long way down. It also makes climbing in and out more of a challenge especially if you are loading and unloading. Every time I climbed up and down the ladder I thought there must be a way to make it lower in the "parked position".

The concept for the trailer I have in mind uses airbag suspension so it can drop down to the ground. The boat is picked up similar to a fork lift and can be dropped off and picked up easily. The idea is similar to a hydraulic boat trailer. I got some slam specialties SS8 airbags - 8 inch diameter, 2.7" collapsed height, 13" max height - the lift range is 10 inches. The idea is to use 2:1 leverage to get up to 20 inches of lift so it can navigate over uneven terrain and hilly ground with more ground clearance. I think the load rating is 2800lbs per airbag. The diameter of the tire is 33 inches.

This is the first time trying to model the drop down boat trailer idea... It's really rough - it's missing fasteners, strengtheners, the balance needs adjusting... needs lots of work. I wanted to make it modular so the i-beams can be unbolted and replaced with different lengths if needed for other projects or if it needs tweaking.

This first design has the airbag in the front and the pivot point in the back. An alternate configuration would be airbag in the back and pivot point in the front.

Twisting moment will be a challenge - I have questions if the twisting force can be overcome.

I picked up a bunch of surplus Aluminum I-Beams and 2x4's for really cheap - so the design focuses on using these sizes frequently.


The back of the trailer is straight like a forklift... Some more strengtheners and cross sections are needed.


The top of the airbag connector needs some work... not finished...

Boat sitting on ground with airbag retracted.

I wanted to see what it looked like with Universal Polyurethane Bushings as the pivot point. The largest I could find was 3 inches long with a 5/8 inch bolt. There are two of them. I have questions if this is strong enough.

Showing boat lifted up with airbag fully extended

This is an alternate design - rough draft - lots of connectors and strengtheners missing... some parts just positioned in place to show the concept...



Airbag retracted - boat sitting level on ground

Airbag extended



I'm concerned about "side sway" - the first prototype will be just used on a farm at low speeds... If possible to refine the design to make it safe for the road that would be desirable.

Does anybody have any suggestions to help reduce "side sway" from the trailing links the wheels are attached to when cornering? I guess the answer to this is related to the strength and free play in the pivot point. I have seen many offroad trailers use an A configuration on the trailing link.