solar electric boat needs more boyancy

If you need different hulls, it makes more sense to build two new ones that are designed for your needs. It will save you time and money. A third hull will also work. As far as steering, at the speed you are operating and the size of the boat, it should not be a critical change.

 

Why not add buoyancy in the amount and position that a good calculation indicates? It shouldn't be necessary to build two new hulls or add a third one.

 

how do I add more buoyancy without changing the original hulls or adding another? I don't understand

 

Well, @TANSL is suggesting adding buoyancy aft, like aft extension and/or sponson or fairing in an aft section. This is also possible, but requires a bit of technical skill to make fair. And it really must be calculated and not guesses.

 

Crudely drawn… but could be done; this is probably way short of need as drawn.

 

See @fallguy picture. Not exactly that but something similar. But should be necessary calculate amount and position.
It is worth considering since it will be much cheaper and faster.

 

I like this idea. it is simple and straight forward. also. I don't really want a third pontoon that will make the boat much bulkier and slow it down.

I'm not sure my skill level is up to this project (I'm more or an electronics guy). is this something a boat repair shop might take on?

 

Honestly, it is pretty technical for most boat shops and they’d charge an awful lot. It is working out in space a bit which is also a bit difficult.

If I were you, I’d start by doing some trim analysis. Determine the proper waterline for the hulls. Then measure the depth on each hull above or below that line with noone onboard on the ends. Then place a known static weight on each hull one foot in on center from the ends where you measured before. I think something like a 40-50 pound weight on each hull would suffice.

Then report the data back here and we’ll see if someone can develop hydrostatics for your little boat.

 

Alternatively, just cut the boat in half, at roughly the midship section - if there is a section that is common to aft and fore sections...and then insert a common sectional shape.
It wont take much to add a central section, in terms of the amount of buoyancy you need/looking for.

 

+1 re Ad Hoc's suggestion - this would probably be the easiest way to go in the long run.
This would mean though that you would probably have to extend the length of your tubular standard Hobie bridgedeck structure, along with the bridgedeck itself.
And you will get the 'most bang for your buck' if you add extra buoyancy in the middle, with an extension of constant section shape.

 

At this point you have probably already realized that you built your boat with the wrong set of hulls and should have been more mindful of all the extra weight that was added by choosing lighter materials and components.

It’s a trap many have fallen into and something I’m always preaching about to those interested in these kinds of conversions.

That said, Classic Hobie Beach Cat hulls are a sealed design and are intended to be submerged, so there’s nothing wrong with riding low in the water although it will slow the boat considerably and make maneuverability more sluggish, and may very likely create instability depending on weight placement and shifting of weight.

Had you kept the original trampoline, used flexible panels, etc.. you probably would have had a 2-4 passenger cruiser.

The best option would be to look for a pair of Getaway or Wave hulls which float a lot more weight before going to the trouble of extending the hulls which would help bring the sterns up, but won’t help with the stability issues much.

I think your idea of a third center hull would be better, but there will definitely be an efficiency and maneuverability penalty that comes with the addition of it.

If you go with a third center hull, I would position it so that the boat sits flat in the water with the outer floats submerged enough so that they keep the boat well pointed, otherwise you’ll be constantly trimming your throttle controls to maintain course. You are right to be concerned about rocking by having the main hull do the majority of work.

In the end, the Classic Hobie hulls just have too much rocker and very little volume where you need it for a conversion like this unless you keep it super light, so I would chalk what you’ve built as a learning experience and take the best ideas and components and retrofit them to a better set of hulls so you and your friends can all safely enjoy.

 

Scott,

Have you considered lightening the load instead of increasing buoyancy?

Your "Deck Chair" is pretty heavy, as is your deck structure.
And the batteries, can you upgrade to lighter, more powerful ones?

 

yes you are right of course. I did not do any calculations at all, just built it and looked to see how it performs. once I moved the batteries to the front it performed OK. I have been on several 50 mile trips and plan to do a 100 mile trip soon. the range of the batteries is just a bit less than 100 miles.

the deck is heavy, but at 67 years of age you won't catch me on a trampoline. the solar panels are light flexible panels so can't save anything there. I built the batteries myself from LiFePo4 cells which are as light and powerful as can be obtained at the moment. lead acid cells are 40% heavier for the same energy rating.

i have used camp chairs which are lighter but don't make that much difference and are much less comfortable, especially on a long trips.

soulmate 1 says that I should just lose 60 lbs. She too is right of course.

I thought of a way to move the deck forward about 12 inches. I would have to cut a channel in the deck for the front of the hobie frame to poke thru, but I think it may be worth it as it will move the batteries forward. I'm going to start work on this tomorrow. when done I will post new pictures of the waterline.

thanks for your interest,

Scott