Non Gasoline Tender

Discussion in 'Boat Design' started by Portager, Aug 21, 2003.

  1. Portager
    Joined: May 2002
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    Portager Senior Member

    I would like to eliminate the need to haul and store volatile fuels onboard Portager, which means finding a means of propelling the dinghy without using a gasoline outboard.

    Rather that listing every option I have considered, I’d rather here your ideas and maybe somebody will think of a new approach.

    My dinghy will be limited to 12’ length by my desire to carry it crosswise on Portager during highway transit, and I want to be able to stow the dinghy sideways and upside down, so the propulsion system will need to be invertible or removable.

    Thanks in advance for any help you can provide.

    Regards;
    Mike Schooley
     
  2. BCBoater
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    BCBoater Junior Member

    Electric trolling motor? Surely on those long passages you'll have lots of alternator power to charge a spare battery. A smallish deep cycle battery should carry you back and forth a 1/2 dozen times before it needs recharging. The battery would be removed before loading and inverting the hull and passed back down into it when it's back on the water. A suitable carry and lowering strap system should make it fairly easy.

    At the risk of seeming primitive may I ask what's wrong with oars? I'm assuming here that the tender is primarily to get back and forth with the groceries and to skip over to parties on the other boats at anchorage close by. If you want it for some up the coast or across the bay runs then forget I posted this.
     
  3. duluthboats
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    duluthboats Senior Dreamer

    Hi Mike,

    Make that 2 votes for a good set of oars.

    Gary :D
     
  4. Portager
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    Portager Senior Member

    Unfortunately I have a narrowed disk in my back and I have learned the hard way that rowing is one is a very good way to really mess up my back.

    I would like to use the dinghy to reach dive sites that Portager can not get to, so it must carry two divers and gear. It must also be able to carry two adults and two large dogs (Great Pyrenees).

    The trolling motors or even an electric outboard would be a reasonable approach, although speed and range would be limited. I would mount AGM batteries, which can be inverted, in the dinghy and bypass the need to transfer them in and out.

    Regards;
    Mike Schooley
     
  5. BCBoater
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    BCBoater Junior Member

    I didn't realize there was a medical reason for no oars. So let's look at the other stuff....

    I'm a diver too and it seems to me that a 12 foot tender for two adults, dive gear and two large dogs is going to be very crowded. Or do the dogs not come along when the other stuff and the Admirable does? Or have you done this already with success?

    With longer trips being taken electric is not so nice an option. Or the larger battery bank would take up too much room and add to the already smallish displacement allowance of a 12 footer. Also I'm not familiar with the term AGM. I'm assuming gel type cells. I know you can put these on their sides but I suspect it would be a good idea to find out if they tolerate upside down storage and if it's OK to charge them in that position. Also I don't know of any gel types that are good for deep cycling like this application calls for.

    Unless you can find a really small diesel outboard I'm thinking you're stuck with gas.
     
  6. yipster
    Joined: Oct 2002
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    yipster designer

    Portager,
    why not list your allready considered options? pedalboat, sail etc?
    in wave's 2 springloaded hinged amas may give propulsion and there must be more ways...

    yipster
     
  7. Portager
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    Portager Senior Member

    What I have considered

    I have considered Diesel outboards, but the Yanmar outboards are too large for a 12’ tender and no longer available in the US due to environmental testing requirements. There is a new Diesel outboard out called the Coventry Climax http://www.dieselmarine.net/ . It is rated at 25 HP, but the weight is 253 lbs, which would be a stretch.

    I considered a two cycle diesel engine/jet drive combination. It is essentially an ultra light aircraft engine with a jet drive. It was very light and power is more than ample (the Admirable would never loose a dinghy race:)) and, since it is a 2 stroke aircraft engine, it could be stored is any attitude. Cost was high compared to a gas outboard, but reasonable for a diesel engine of comparable horse power. The down side is the mean time between overhauls is relatively low, parts and service availability is non existent and the effort to integrate it into the dinghy would be substantial.

    I looked at using multiple trolling motors or electric outboards and AGM batteries.

    As a side note to BCBoater;

    AGM stands for absorbent glass mat, the electrolyte is confined in an absorbent glass mat with the excess electrolyte removed (starved electrolyte). The battery is valve regulated, which means there is a pressure relief valve that prevents excessive overpressure, but unless grossly over charged, it remains closed. AGM batteries use recombinant technology (which means there is a catalyst that recombines the electrolyzed hydrogen and oxygen before it escapes), same as gel cells. One of the key advantages of AGM batteries is that since the plates are wedged between glass mats and the case they do not need to support the bending loads that flooded lead acid and gel cell plates experience. This means that the plates can be made of weaker lead alloys which have lower internal resistance. The lower internal resistance makes then more efficient to charge and discharge (less energy is wasted) and since less heat is produced they do not get as hot so they can be charged much faster than flooded lead acid or gel. IMHO AGM batteries have made gel cell batteries obsolete and the only advantage flooded batteries have over AGM is cost.

    AGM batteries can be deep cycled, in fact the Optima and Hawker Genesis batteries are the only batteries I know of that can be discharged 100% without accelerating their end of life, provided you recharge them promptly at >25% of their amp hour capacity per hour (i.e. a 40 AH battery should be recharged at > 10 amps in bulk charge mode). The Hawker Genesis has a rated life of 800 cycles at a 50% depth of discharge and 400 cycles at 100% depth of discharge. One way to look at it is you could install half as many batteries and replace them twice as often, so you go through the same number of batteries. The advantage is the usable capacity per pound is much higher is you discharge 100% instead of the recommended 50% for conventional batteries.

    The electric outboard would allow the dinghy to reach reasonable speed (plane) although getting much range would require slowing down to displacement speed (i.e. 4.5 knots) and multiple batteries. The problem is most high power electric outboards use 48 or 60 VDC (i.e. 4 or 5 - 12 volt batteries in series). I am planning to configure Portager using 24 VDC power and I could recharge the dinghy batteries at high rates at 24 VDC, but recharging a 48 VDC or 60 VDC bank would require some additional thought. I’m thinking I could configure the dinghy with 2 24 VDC banks that would have a two way combining switch. One position of the combining switch would combine them in parallel for charging and the other would combine them in serial for operation. I would mount the connector to plug into boat power where it would interfere with the combiner switch unless it is in the proper position.

    I have gone diving in an 11’ Zodiac with three divers and three sets of gear. It was crowed, however the boat was able to plane with a 15 HP outboard and we routinely traveled several miles up and down the coast, so I think 2 divers in a 12’ dinghy (of the right configuration) should be adequate. No, the dogs don’t need to go on the dive trips, just on trips to shore with the Admirable and myself.

    Regards;
    Mike Schooley
     
  8. Doug Carlson
    Joined: Feb 2003
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    Doug Carlson Senior Member

    Mike,

    Do you have a reference for this arrangement: "a two cycle diesel engine/jet drive combination"?

    Doug Carlson
     
  9. Guest

    Guest Guest

    If electric, I believe the eCycle is shipping now?
    <img src="http://www.ecyclemarine.com/side_v_silver.jpg" border="0" alt="">

    At $4000US, so about 2x price of 9.9hp 4-stroke. But only 60lbs to heft about vs 100+lbs for the gassers. And all that other stuff about noiseless and odorless and vibrationless...

    Batts? Yeah, split the pack for charging.

    Batts weight? Well, short distances and slower speeds, or move to newer chemistries rather than lead acid. The EV (car) folks are getting pretty excited about the NiZh and NiMH stuff... LIon polymer stuff too. It's all about the charging algorithms and battery management systems... oh yeah, and keeping the water out <smile>

    Lock
     
  10. BCBoater
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    BCBoater Junior Member

    Thanks for taking the time to type out that explanation for the AGM batteries.

    I like what you're describing for the setup too. The batteries could probably fit down into a central inboard "keel" box that would act as a seat and strong back for the tender.
     
  11. Portager
    Joined: May 2002
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    Portager Senior Member

  12. Portager
    Joined: May 2002
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    Location: Southern California

    Portager Senior Member

    Electric Catamaran Dinghy?

    I found an electric vehicle battery comparison at http://www.princeton.edu/~chm333/hybrids/electric/battery.htm . It indicates that, compared to conventional lead acid batteries, modern SAFT NiMH batteries could provide twice the range and 3 times the cycle life, but would cost 8 times as much. Lithium Ion batteries would provide 3 times the range, about the same cycle life but cost 9 times as much. Lithium polymer would provide 4 times the range, about the same life cycle, but cost 10 times as much. The higher life cycle cost of the advanced batteries partially offset the higher cost, however, the increased range still costs a significant premium.

    In my case, the cost trade would be even worse since I would not use the higher cycle life before the batteries succumbed of old age, therefore I would choose the advanced lead acid batteries.

    I’m thinking the best way to extend range would be by using a more efficient hull form. Therefore, I am leaning towards a, dare I say it, Catamaran, which would be efficient to propel and provide ample space for dive gear or dogs. I’m thinking of narrow hulls, just wide enough to hold the batteries and a nearly flat bottom for beaching. Total length would be 12’ and beam about 5’ to 6’. Does anybody know of an existing design that would be close?

    The eCycle outboard looks like a good option, although I think it is really a 6 HP motor, but they claim the dual props provide the thrust of a 9.9 HP. The dual props should provide a benefit, but I think it would be closer to that of a 8 HP than 9.9.

    Regards;
    Mike Schooley
     
  13. Portager
    Joined: May 2002
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    Portager Senior Member

    I'm still looking for a suitable hull for an Electric Catamaran Dinghy if anyone knows of anything that might be close I'd really appreciate it. :D The main requirement is the 12' length limitation and the payload which I estimate at ~1000 lbs (600 pounds of people/gear/dogs, 263 lbs of batteries and the remaining 137 lbs for the electric outboard and misc.). The battery compartment in each pontoon would be 6.525" wide, 6.93" high by 34.3" long worst case.

    Thanks;
    Mike Schooley
     
  14. Willallison
    Joined: Oct 2001
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    Willallison Senior Member

    What you need is an aluminium hulled, semi-rigid collar (as opposed to inflatable tubes) cat, with a drop-down bow section (a-la landing barge) to ease diver (& dog) entry/exit, powered by a small high-speed diesel driving through a water jet. :idea: :D
    Never seen one :(

    Why the twelve foot LOA?

    When you dive - are we talking free dive, scuba or compressor? If you went the electric route and don't want to go too deep, I can recomend a powerdive unit (
    http://www.powerdive.com.au/default.asp?fv=6&b=IsIe5&d=1pageredirect=default.asp ) Small, light, quiet and easy to use. What's more, it could run off the boats own power supply. The biggest problem I see with your electric tender is weight - slows you down, makes launch and recovery a more precarious occupation and adds to your overall towing burden.
    I'm surprised you manage to plane in an 11' zodiac with 3 divers + gear aboard. We use an 11' Avon with 15hp. It just planes with 3 people and 2 sets of scuba gear - but not 3.
    I wouldn't have anything but an inflatable (or collar) as a tender - much kinder on the mothership, way safer than a traditional hard dinghy, virtually unsinkable, but most of all, very stable - which is very important when you're clambering in & out of the water with dive gear on - and equally important when you've got 2 energetic pups who are excitied about going ashore... :p
     

  15. Willallison
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    Location: Australia

    Willallison Senior Member

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