Micro Aquatic Vehicle

[thomprice]

Greetings,

I'm new to the forum but I look forward to reading your responses to this design. I was living in Venice, Italy and I came up with an idea for a small outboard motorboat that could be used like a motorbike would be used on a road: to transport 1 or 2 people for pleasure rides or for commuting. You might think that a jet-ski would be the nearest thing, but when I think of a jet-ski, I think of getting all wet, and in Venice, that might not smell too good.

My design is completely enclosed, with a sliding roof for entry. It is based on the classic lines of the 40's and 50's using a barrel-back stern and the windshield/roof look like a classic French Citroen.

You can take a look at the design here (http://www.createthefuturecontest.com/pages/view/entriesdetail.html?entryID=286).

I've designed the boat to be built with plywood (all surfaces are developable) and one possible method of construction could be Stitch-n-glue. After taking a look around the forum here, I see that there are some very strong opinions on this topic, and I can already imagine some of the comments. Let me just say that I've used this technique with similar hull shapes before (also my own designs) and I am rather fond of it.

I hope you like this new design and I look forward to reading your comments.

Thanks,
Thom Price

[kenjamin]

Thom,

Greetings and welcome to the forum. I applaud your imagination. It looks like a cute little thing. How much horsepower were you thinking it needed? It looks like it would be no easy build. I guess if you just had to be completely enclosed (for your passenger to use a laptop on the way to work or something) it would be a solution. I think for about the same money one could build a nice Rascal – but of course you'd have to bag the computer until you got to work. The Rascal does have the air through the hair thing going on and a much lower center of gravity. Take into account that I am a prejudiced Mazda MX-5 owner.

[Lewisboats]

Interesting altho a bit top heavy if I may say so...a bit wider and a bit lower might improve the ride and safety. Keep up the good work. Please show us some of your other work :D

Steve

[thomprice]

I was thinking of a Honda 20, which I believe would be plenty of power for planing with two people aboard. The addition of onboard computer or laptop/handheld docking station is amusing, but I'll hold off on the prototype. The center of gravity is actually not very high considering the relative width of the bottom (in comparison to a more traditional round or V hull) and the center of buoyancy. Naturally the CoG can be controlled very easily with the thicknesses of the panels that are used (ie: half inch for lower part, quarter inch for upper). On such a small boat, CoG is effected greatly by the number and size of people on board and where they are located. I don't see it being any more of a problem than CoG is with a motor bike - it is just a matter of leaning.

[kenjamin]

Except that on a motorcycle you have the stability of the two rotating wheels and no boyancy to overcome. In that small enclosed space is there room for leaning? Still, I find your design entertaining and interesting. If it were lower and wider there would be less concern about it tipping over. If it tipped over there would be water pressure against the closed door making getting out more of a problem.

[Tar Devil]

Cute design and fun concept, but boarding and deplaning will be problematic.

[willmarsh3]

I think it's a really neat design concept.

I would say to take it to a naval architect but it appears you are interested in learning about designing boats and taking this to a finished design. To point you in the right direction here's a long and fascinating thread on this forum that illuminates what is involved in the boat design process.

http://www.woodenboatvb.com/vbulletin/upload/showthread.php?t=12184&highlight=perfect

[Spokaloo]

Its a good foundation to start from, definitely.

I think windage might be an issue, but one easily mitigated with round shapes and no sharp edges in the above-gunnel areas. To reduce any topheaviness issues, Id think a wood hull with a foam superstructure (blasphemy on this forum, but widely recognized elsewhere) would really suit it well.

E

[thomprice]

These are very helpful comments! I think that maybe the images may be misleading regarding the proportions because they are not in plane view. However, I certainly will pay close attention to the CoG. Windage could be more of an issue than with very heavy boats. That's certainly the case with my Toyota Yaris, but then again, I don't mind so much because I'm getting 40+ mpg. I doubt that either will flip over unless highly provoked.
After reading some of the comments, I've been thinking of replacing the rigid roof with a rag top, which would decrease the weight, ease accessibility, and be less likely to trap someone in if there were an emergency.
The foam core sounds interesting, but I'm trying to think how thick it would have to be in order to achieve the same resistance to puncture as 1/4" plywood with biaxial glass and epoxy, which is also very light.

Thanks again,
Thom

[kenjamin]

Somehow a rag top sounds good to me!:D

[paladin]

a two part sliding collapsing canopy of lexan would cure the problem with external water pressure if the device tipped over...all movement would be fore and aft.....at 10 feet long with about 8-10 hp the unit should plane with two people if the hull is properly built......a lower center of gravity could be achieved by making two plywood boxes as the trusses around which to construct the hull, allowing the two passengers to sit lower between the rigid panels. Full control could be a unilever side stick controller with HOTASS control...complete with starter and kill switch.

[Spokaloo]

As for the foam, I would prob go with divinycell. Using that core, the glass doesn't need to be terribly thick, as this will not be a portion of the hull. Puncture resistance is far more important in the water than out. I think ply is the only way to go from the gunnels down, as wood has so many great attributes.

For the cabin, though, foam is light, and would require only a moderate skin for strength, abrasion resistance, and smooth appearance. Unless you plan on augering into trees and such, I wouldn't worry too much about puncturing your cabin.

If you build just the upright sections with foam, do a large lexan windscreen, and a canvas top with canvas aft curtain, you get a convertible thats heatable, with extremely light weight, good weather protection, and the best of both worlds as for space and materials usage.

E

[paladin]

The advantage of using plywood panels from the gun'ls down would be a good way to go as you really don't need smooth curves as such and a developed hull is easy. Use divinycell or klegecell for the entire upper shell and you can heat it with heat lamps to take the curves for a female mold.

[George Roberts]

thomprice ---

Difficult to determine scale and suitability.

I suppose that the design allows the occupants' feet to rest on the skis. I suppose the scale/shape of the tunnel simulates the shape of a motorcycle.

There appears to be a lack of lateral resistance that a motorcyclist might enjoy.

The devil is in the details.

[kengrome]

To reduce any topheaviness issues, Id think a wood hull with a foam superstructure (blasphemy on this forum, but widely recognized elsewhere) would really suit it well.

I would agree with this except for one thing. When the upper hull can be built with 1/4 inch or thinner plywood, foam will weigh more than the plywood after it gets a layer of epoxy and glass on both surfaces and is then filled and faired.

I built the main hull of my little 8 foot 'paddle banca' in 1/2 inch thick styrofoam because I thought it would be lighter than 1/4 inch plywood. Unfortunately it is heaver. It took a lot more time to build and it cost a lot more than plywood would have, too.

I was going to build the amas out of foam / epoxy / glass as well, but after learning how much extra weight, work and money was invested in the main hull, I decided to make the amas out of plywood. They were fast and cheap to build ... and they are light!

I think the weight saving available when using foam core is only possible in larger boats that require thicker plywood for the superstructure.

I will never try to 'save weight' by using foam again on such a small boat-- not when 1/4 inch or thinner plywood will do.

[kengrome]

By the way, I like the design concept!

:)

[Spokaloo]

Ken, there are two key concepts here that might be askew.

First, Styrofoam and Divinycell/Klegecell are VERY DIFFERENT foams.

Secondly, you can use the same skin you would have used over the ply to cover the foam. Being that it is above the waterline it does not have to carry the overall thickness and abundance of epoxy that a hull would.

It would, in fact, be a lighter superstructure.

BTW, how is the tolman coming?

E

[kengrome]

Ken, there are two key concepts here that might be askew. First, Styrofoam and Divinycell/Klegecell are VERY DIFFERENT foams. Secondly, you can use the same skin you would have used over the ply to cover the foam.Yep, there are major differences in these foams. For starters my styrofoam is lighter than both of them, and they are both stronger than my styrofoam.

But remember, I was not talking about covering the ply with epoxy and glass. Ply doesn't need any epoxy / glass sheathing, that's why it is lighter.

Of course if you're going to cover the ply with epoxy and glass anyways, it will be heavier than the foam ... but it will still cost a lot less unless you use cheap styrofoam like I did.

:)

[thomprice]

I'm wondering how much of a difference foam could have over plywood with regards to weight, being that we are only talking about circa 20 sq. ft. of material. It is also an area that has to be stepped on and I would think that the few pounds that it would save wouldn't be that great of an advantage considering the lower weight bearing capacity. My guess is that it is better to INCREASE the weight of the bottom, than to DECREASE the weight of the top. The end result is the same, and the boat is much stronger.

[Spokaloo]

Thom, you are targeting for a combination of strong and light. You increase scantlings for the places that need it (as in where you are stepping on the boat) and you reduce them where they are not needed, such as vertical structures in the cabin.

There are various books on the topic as well, many of which are provided at our host's site.

E