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Thread: A few questions from a hovercraft newbie

  1. #1
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    Default A few questions from a hovercraft newbie

    Hi all



    I have bought a robin ec25ps engine and are hoping to build my first hovercraft along the lines of the simple cyclone / challenger design.

    I am fortunate enough to have in my possession a copy of the HCGB constructors guide and a copy of a technical publication by nigel beale on breeza fans for hovercraft, so I have some solid information available.



    I am hoping to use polaris parts to increase the performance of the ec25 from 20 to 30+ Hp to get a powerplant with a good power to weight ratio.



    Currently I am planning a 6 by 10 ft craft with an absolute maximum (all inclusive) weight of 600 lbs. It will have a finger skirt and be very similar to the example hovercraft described in the hovercraft constructors guide.

    Hopefully the craft will be an integrated design on a htd reduction system running a 800mm either 4z or 5z multiwing fan.



    Can anybody give me advice on the use of the EC25 for an integrated design craft? Am I wise to use polaris parts to get it up to over the 30hp mark (performance parts are available to get it up to 38hp) and lastly do my facts and figures seem plausible, forgive me if they are not, this will be my first craft remember



    Thanks in advance for your help.



    Bruce

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    Default Re: A few questions from a hovercraft newbie

    Hi Bruce,



    The Simple Cyclone is now considered a very old design of craft and the EC25 is not exactly a modern engine.

    If you want an efficient craft that is safe, efficient and reliable I would look at more modern alternatives.

    You don't want to build something that you won't enjoy using in the end.



    I would recommend contacting the Hovercraft club of NZ and speaking to people who have built craft recently and finding out what is available and what works well. Alternatively contact the Australian hovercraft club.



    An 800mm duct is by modern standards quite small. Most craft use 800-1200mm ducts and many use propellers.

    In the UK and US four stroke industrial engines of 22-40hp are most popular as they are simple to install and very reliable. These are available from Briggs & Stratton, Kohler, Honda and Kawasaki.

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    Default Re: A few questions from a hovercraft newbie

    Hi, Thanks for that response.



    Is 800mm quite small even for a small engine (40hp or less)?



    Also what were the problems with the Cyclone craft? (you mention safety)



    Were there relaibility issues with the EC25?



    To my knowledge the Hovercraft Club of New Zealand ceased to exist some years ago due to not enough interest

    (As a youth I had a family member in the club so I have seen a number of craft in action)



    I Have a set of plans for a superwedge and for some UH designs but I want to stick with something not too big first up and I arent too keen on the UH designs.



    Unfortunately I am kinda committed to the engine now, I bought it specifically for this project. (Brand New can you believe it) On the up side after Fuji Robin stopped producing it in the mid 80's it is my understanding that polaris kept using variants of it in there ATV's right up to 97. This means that a number of parts are still available.



    I would have prefered to go with the engines mentioned but unfortunately that size arent too common in New Zealand. Sure you can buy a 25hp Briggs, but expect it to cost probably $3000, which is a good portion of my project budget.



    Let me put my questions another way then.

    If I were in the UK and starting out building my first craft on a modest budget, what would members of the HCGB be reccomending that I build?



    Thanks Again



    Bruce




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    Default Re: A few questions from a hovercraft newbie

    Hi Bruce

    There's nothing wrong in what your proposing - its a question of managing your expectations. Todays integrated cruising craft closely follows the 1974 Simple Cyclone design (indeed it is the original integrated craft) but with more reliable 4 stroke engines, mostly with more bhp, probably a bit bigger lift area to carry more and keep cushion pressure down, a bit more freeboard and buoyancy to float better on water.



    As a result todays cruiser would expect to cruise 50 miles in a morning in fairly open conditions over salt water without problems whereas craft of the late 70s expected to break down in a day spent in a field and a pond. Todays craft you would expect to be fibreglass and full of shapely curves compared to the boxy shape of a plywood Simple Cyclone. But much of it is cosmetic and as long as you meet the weight targets and keep it well painted ply is fine.



    I'd increase the length (width if poss) and hull height by say 10 -20% put in plenty of bouyancy and crack on. But expect just to use it in sheltered conditions, school field, local lake river etc with reasonably flat water entry - but you could still have a lot of fun. The EC25 is now a pretty old engine and only surfaces on older craft so I'm not sure what expertise there is now on uprating it - but someone might pop up with info.



    Good luck

    Keith

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    Default Re: A few questions from a hovercraft newbie

    Hi Bruce I have seen a 3/4 size Turbo Superwedge powered by a EC25pm engine and it works great for a single Occupant..



    Regards



    Tony.W.

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    Default Re: A few questions from a hovercraft newbie

    Hi Bruce,



    Many of us are using 35hp engines and we all use 900mm ducts minimum. 6 years ago I had a racing craft with 40hp and a 750mm duct. I fitted a 900mm duct and it transformed the performance.



    I can't comment on the EC25s reliability. I used to have one but never used it because there was always something better to use.



    My concerns on safety with a Simple Cyclone would be the low freeboard and low buoyancy if you were to use it on open water.



    Look at some of the Ausie craft and see what you think.


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    Default Re: A few questions from a hovercraft newbie

    With Regards to buoyancy and freeboard;

    I will use either polystyrene or urethane foam inside the hull to give a safe level of floatation. If I were to make the depth of the hull 300mm would this be sufficient freeboard, If not what would you reccomend?



    Thanks



    Bruce

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    Default Re: A few questions from a hovercraft newbie

    300mm absolute minimum to the bottom of the duct in an integrated craft. Go for a deck height of at least 500mm.

    Put extra buoyancy at the rear and under the duct.

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