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Thread: Jetski Engine As An Inboard

  1. #1
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    Default Jetski Engine As An Inboard

    Small new inboard engines of 50 to 100 hp are fast becoming extinct except for diesels which are extremely expensive. If anyone disagrees with this, I would like to know where you've found them. In any case, I'm wondering if anyone has ever adapted a PWC engine (without the pump) as a "true" inboard operating at a 10 degree shaft angle and with a transmission, either an 8 degree down angle or no angle.
    The mass of men lead lives of quiet desperation......Thoreau

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    Default Re: Jetski Engine As An Inboard

    Someone tell me why the following won't work:

    Picture a 50 hp 2-stroke PWC engine driving a 10 degree angle prop shaft through a heavy duty centrifugal clutch (made by North American Clutch). Add a heavy duty roller clutch with pulley to the drive shaft output side of centrifugal clutch. Add a 12 VDC automotive type starter motor with pulley and belt drive to the roller clutch pulley. Add an electric 12 VDC water pump to cool the engine. We need a 12 volt battery anyway to start the engine.....it can also serve the 12 VDC automotive type starter motor when REVERSE propulsion is needed so........FORWARD propulsion is merely a function of engine RPM/centrifugal clutch (direct drive).....REVERSE is merely a switch on the dashboard turned on when engine is at idle.....engine turns CCW rotation, starter motor turns CW rotation. The two clutches would be in an assembly that would include a thrust bearing to handle prop thrust load and would include the shaft coupling. Gasoline = forward, Electric = reverse.......this is the same as my 76" X 18" "Rosita" radio controlled model will use except in the case of the model, I used an electric clutch instead of roller clutch 'cause I didn't think of the latter early on. Comments would be appreciated.....if you haven't guessed by now, this whole idea revolves around "Slippery" .......see elsewhere here.
    The mass of men lead lives of quiet desperation......Thoreau

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    Default Re: Jetski Engine As An Inboard

    Not sure what you mean "without the pump", isn't that what drives it? but there was an article in WB magazine a while back about a guy in Ct. I think who built a down east style boat using a PWC motor. If I remember correctly he stated that you couldn't buy a bare PWC motor so he ended up buying a complete PWC and removed the motor from it, basically he built the boat around the motor, the only complaint was that in shallow water it sucked up a lot of bottom debris, personally I think it's a neat idea.

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    Default Re: Jetski Engine As An Inboard

    Maybe five years ago there was an excellent WoodenBoat Magazine article on this. A fellow wanted a sort of "spirit of lobsterboat" but small in a light planing hull and the permanent berth had very little water. They toyed with all sorts of ideas before hitting on power by jet ski. For that project, it worked out cheaper to simply buy a jet ski, extract the engine and drive, and toss the hull. Anyway, it worked.

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    Default Re: Jetski Engine As An Inboard

    It was Tommy Townsend of Thomas Townsend Custom Marine Woodworking that had the lobsterboat with the jetski engine in it. It was on the cover of WoodenBoat # 198.

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    Default Re: Jetski Engine As An Inboard

    Good catch Steven.

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    Default Re: Jetski Engine As An Inboard

    What sort of boat are you talking about using this on John? A keel-boat? Fishing boat? Pontoon boat? Punt? House boat?

    Why throw the jetski away at all?

    I can’t find a picture of them but I’ve seen pontoon boats and small work barges, built here in Oz, driven by jet ski’s that can be docked/un-docked in the same way as this RIB:

    Larks

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    Default Re: Jetski Engine As An Inboard

    I think what the OP means by 'without the pump' is using the engine to drive a shaft/running gear/prop, i.e., instead of using the waterjet drive and impeller. A transmission may be necessary depending.
    "It ain't what you don't know that gets you into trouble. It's what you know for sure that just ain't so."

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    Default Re: Jetski Engine As An Inboard

    This 50 hp PWC engine will be a 2-stroke thus no concern about lubrication of the engine installed at a 10 degree shaft angle......and yes, I want it to drive a prop shaft (NO JETDRIVE PUMP). I'm wanting to build the little 14'3" Hacker stepped bottom hydroplane "Slippery" as I have talked about on this Section of the Forum and I think the PWC engine will do the trick as Hacker specified a 40 hp Lycoming engine. I will need some guidance on prop selection, that's for sure, so obviously there's more research to do. I don't want to use a transmission......and if I did, I would want 1:1 ratio in forward so why not eliminate the transmission altogether? and, as described above, reverse is accomplished with ROLLER clutch and a 12 volt electric motor spinning clockwise direction.
    The mass of men lead lives of quiet desperation......Thoreau

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    Default Re: Jetski Engine As An Inboard

    I don't think props in water go well at 8000 rpm. And your 12v reverse power will be totally different characteristics.

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    Default Re: Jetski Engine As An Inboard

    Yes you can. It would be easier to just put an Evinrude Etec on the stern of course.
    If you want you can emulate the old speedboats from the GDR. Wartburg 900-1000cc 2stroke 3 cylinder 50-100hp motor, thrust bearing, prop. Usually no clutch, raw water cooling via propellor back pressure, no reverse. Not that I recommend this setup, but the engines are still available in Germany. Nowadays many are converted to the conventional setup of dual circuit cooling and transmission.

    New 2 stroke engines can be had from the UL flying people, motorcycles, outboards, snowmobiles and of course PWC. It does not pay to muck around with multiple clutches, a normal transmission with reverse and integrated thrust bearing is best. Also a engine driven cooling pump solves the cooling rate because it is coupled to rpm's, no controller needed. But you can eliminate the transmission, use direct drive, and take a paddle for reverse.
    If weight is paramount then the UL engines are best. Examples: Rotax 582, 65Hp, weight 65lb. Rotax 600 Etec, 118Hp, 75lb (naked engines weights. Real world weight is higher).

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    Default Re: Jetski Engine As An Inboard

    Quote Originally Posted by John A. Campbell View Post
    This 50 hp PWC engine will be a 2-stroke thus no concern about lubrication of the engine installed at a 10 degree shaft angle......and yes, I want it to drive a prop shaft (NO JETDRIVE PUMP). I'm wanting to build the little 14'3" Hacker stepped bottom hydroplane "Slippery" as I have talked about on this Section of the Forum and I think the PWC engine will do the trick as Hacker specified a 40 hp Lycoming engine. I will need some guidance on prop selection, that's for sure, so obviously there's more research to do. I don't want to use a transmission......and if I did, I would want 1:1 ratio in forward so why not eliminate the transmission altogether? and, as described above, reverse is accomplished with ROLLER clutch and a 12 volt electric motor spinning clockwise direction.
    John anything can be done with the right engineering.
    There is a world of RPM difference between the 40hp Lycoming and the 50hp Jetski engine - the Lycoming is maxed at about 2500 (I guess) whereas the jetski 2stroke will probably do 8000 plus.
    But for a hot rod boat such as the Hacker, it may suit.
    In its favour it has a cooling system with the engine manifolds in place, and it is built for marine use - so very good choice there.
    The Lycoming 40hp was originally an automotive engine I believe, but I can be corrected.
    Choose your Jetski engine and get the power curve - how many rpm on one axis and the available shaft horsepower on the other.
    Then work out the prop gap - available diameter for the propellor, twice the distance between the keel and the shaft at the propellor.
    Then you can work on the prop choice, but I think because of the high rpm you will need some extra advice.
    Then go an speak to an out and out inboard Hydroplane racing enthusiast, preferably one who owns a boat, as they are the experts in high speed engines, direct drive, minimum rudders, water pickups and high rpm props.
    The good news is that there are guys out there who have developed the underwater gear (the work has already been done) you need for your new boat.
    Go for it.
    Last edited by Don MacLeod; 07-17-2017 at 12:35 AM.

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    Default Re: Jetski Engine As An Inboard

    Quote Originally Posted by John A. Campbell View Post
    Someone tell me why the following won't work:

    ...the 12 VDC automotive type starter motor when REVERSE propulsion is needed so........
    I normally prefer to be suggesting ways around problems that are supposedly insoluble, but this time I'm dumping a bucket of ice cold "that won't work" on part of the idea.

    Starter motors generate lots of torque by drawing lots of current. That means they heat up very quickly. To avoid it's early demise, you need to adhere to a 1% duty cycle, with about ten seconds maximum run time. So you're looking at waiting at least ten minutes for the starter to cool down before your next 10 second burst of 0.5 HP in reverse.

    The end result would be similar to a large vessel trying to use it's jacking engine for reverse.

    regards,
    Joe
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    Default Re: Jetski Engine As An Inboard

    Quote Originally Posted by slowpoke View Post
    I normally prefer to be suggesting ways around problems that are supposedly insoluble, but this time I'm dumping a bucket of ice cold "that won't work" on part of the idea.

    Starter motors generate lots of torque by drawing lots of current. That means they heat up very quickly. To avoid it's early demise, you need to adhere to a 1% duty cycle, with about ten seconds maximum run time. So you're looking at waiting at least ten minutes for the starter to cool down before your next 10 second burst of 0.5 HP in reverse.

    The end result would be similar to a large vessel trying to use it's jacking engine for reverse.

    regards,
    Joe
    That is true for an old school series-wound direct drive starter, much less so for a geared starter (almost any Toyota), and I think some of these also use permanent magnets instead of a stator winding.
    And realistically, you aren't going to spend much time in reverse anyway. I think it would work fine, but why not just use a paddle?

    Pete
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    Default Re: Jetski Engine As An Inboard

    Quote Originally Posted by John A. Campbell View Post
    Small new inboard engines of 50 to 100 hp are fast becoming extinct except for diesels which are extremely expensive. If anyone disagrees with this, I would like to know where you've found them. ...
    What weight of engine was the boat originally designed to take?

    Complete, ready to run VW beetle engines are available for reasonable money - right sort of horsepower, reasonable weight, lo-line installation - dunno about a marine gearbox....
    Someday, I'm going to settle down and be a grumpy old man.

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    Default Re: Jetski Engine As An Inboard

    I really don't know jack about engines. But won't this thing be really really loud? PWCs certainly are.

    Jeff

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    Default Re: Jetski Engine As An Inboard

    This quest for a small inboard engine for my planned Hacker "Slippery" 14'3" X 4'9" step bottom hydroplane has become an exercise in excitement and a bit of frustration. Currently I'm looking at two options.....both expensive. First is the G.M. based 1.0 liter 75 hp Ecotech marine engine coupled to a ZF 15M transmission for $8500. Second is the Kohler LH775 30 hp liquid cooled commercial engine coupled to ZF 15M for around $5500. I'm waiting for info from a reputable naval architect as to performance that I could expect from either engine. A keel cooler is recommended for either choice. I've been in communication with a person who has good solid experience with both setups. I know it's crazy to get so damned caught up in a little boat like this but I've wanted to build a full size Hacker for 34 years and I'm in love with "Slippery"....I've got room enough in my shop to build her and room in an outbuilding to keep her protected from the elements. I'm currently in the last stages of building a 76" X 18" R.C. gas/electric model of Hacker's "Rosita" and on 10/1/17 I shall begin lofting "Slippery" full size.
    The mass of men lead lives of quiet desperation......Thoreau

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    Default Re: Jetski Engine As An Inboard

    A keel cooler on a step hydro seems like incompatible technologies to me. Wouldn't any flowthrough be too rapid for heat exchange? Wouldn't the significant drag be something to avoid as well?
    "It ain't what you don't know that gets you into trouble. It's what you know for sure that just ain't so."

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    Default Re: Jetski Engine As An Inboard

    Quote Originally Posted by rbgarr View Post
    A keel cooler on a step hydro seems like incompatible technologies to me. Wouldn't any flowthrough be too rapid for heat exchange? Wouldn't the significant drag be something to avoid as well?
    I thought about that the same way......I don't see why cooling the engine with raw lake water wouldn't be better......then, would you want to use a separate electric water pump to pull water through a "screened intake port" on bottom of hull (can't remember the correct name for that "attachment" on hull bottom) or drive a pump from a pulley on the engine? From what little I know about heat exchangers, they seem to have the same characteristics as keel coolers and would have similar disadvantages. I really need some good advice on this......many thanks!
    The mass of men lead lives of quiet desperation......Thoreau

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    Default Re: Jetski Engine As An Inboard

    You might try to find a hydroplane forum for your types of questions. They'd have more experience with addressing and solving them.
    "It ain't what you don't know that gets you into trouble. It's what you know for sure that just ain't so."

    -Mark Twain

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    Default Re: Jetski Engine As An Inboard

    Quote Originally Posted by rbgarr View Post
    You might try to find a hydroplane forum for your types of questions. They'd have more experience with addressing and solving them.
    That was excellent advice....I went to Google and put in "step bottom hydroplanes" and very quickly found an article that really cooled my ardor toward "Slippery"....I now know how she got her name.....step bottom hydros are often unpredictable and dangerous. Now I'm thinking about building her without the step and I'm not real comfortable with that as I don't like the idea of screwing around with any naval architect's designs much less Mr. Hacker's......so now what?......suggestions will be very much appreciated.
    The mass of men lead lives of quiet desperation......Thoreau

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    Default Re: Jetski Engine As An Inboard

    Someone here has written all about building one of these if I recall correctly: https://www.woodenboat.com/boat-plan...unabout-rascal
    "It ain't what you don't know that gets you into trouble. It's what you know for sure that just ain't so."

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    Default Re: Jetski Engine As An Inboard

    JA you might be getting on the right track.
    That "G.M. based 1.0 liter 75 hp Ecotech marine engine coupled to a ZF 15M transmission" to a correctly sized prop might give you the zing you desire.
    More HP and rpm the original Lycoming inboard. It should fly. And I think will be a lot better proposition than a JetSki two smoke.
    I am surprised that with a stepped hull it is suggested to go with keel cooling.
    To me that is for slow displacement hulls where you have constant cool water flow past the hull. They work well in that situation.
    A stepped hull has a lot of air going under it, and will generate air time which suggests a transom or rudder based water pickup to a heat exchanger inside.
    The challenge you have is that today fast small inboards are "an old product" of a bye gone era....and the expertise to build them is slipping away fast.
    Keep us posted.
    Is your model gas engine water cooled or air cooled?


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    Default Re: Jetski Engine As An Inboard

    Quote Originally Posted by Don MacLeod View Post
    JA you might be getting on the right track.
    That "G.M. based 1.0 liter 75 hp Ecotech marine engine coupled to a ZF 15M transmission" to a correctly sized prop might give you the zing you desire.
    More HP and rpm the original Lycoming inboard. It should fly. And I think will be a lot better proposition than a JetSki two smoke.
    I am surprised that with a stepped hull it is suggested to go with keel cooling.
    To me that is for slow displacement hulls where you have constant cool water flow past the hull. They work well in that situation.
    A stepped hull has a lot of air going under it, and will generate air time which suggests a transom or rudder based water pickup to a heat exchanger inside.
    The challenge you have is that today fast small inboards are "an old product" of a bye gone era....and the expertise to build them is slipping away fast.
    Keep us posted.
    Is your model gas engine water cooled or air cooled?

    I don't believe the fellow who recommended keel cooling really understood "Slippery's" design....I'm pretty sure he was basing that recommendation on those Louisiana 17-20 foot aluminum mudboats where he has used the 1.0 liter Ecotech engine and ZF 15M with very good results. The engine in my Hacker "Rosita" model is a water-cooled 30 cc Zenoah with on-board electric starter controlled from transmitter. This is a BIG model....18" beam and 76" overall length....she weighs 44 pounds and I am really concerned that the Zenoah won't be able to push her at scale speed. I have 866 hours in her right now and probably another 100 to go.......she is the 8th radio controlled Hacker model I've built over last 20 years. She will be trailered in an ornate wooden box mounted on my Castlecraft aluminum canoe trailer built along the lines of Jim AAmodt's "Classic Boat Trailers"....totally enclosed...to transport, show, and launch her.
    The mass of men lead lives of quiet desperation......Thoreau

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    Default Re: Jetski Engine As An Inboard

    Also, about my "Rosita" model, water to the Zenoah will be pumped by a Sonic-Tronics SOT1260 12 vdc "smoke pump" normally used in model aircraft to generate smoke patterns in flight. Sonic-Tronics modified this particular unit to work off 12 volts. I don't see why a similar cooling method for "Slippery's" engine wouldn't be advisable......might want to increase the size of the 12 volt starting battery and I can't believe a 12 volt self-priming water pump of good strong velocity would be that hard to come by. I'm not at all interested in water pressure from the prop or forward motion of the boat forcing water to the engine.....I want a good steady flow of clean lake water to that engine with it's discharged water down the exhaust with the boat standing still and engine idling and someone tell me why an electric pump is not the answer.
    The mass of men lead lives of quiet desperation......Thoreau

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    Default Re: Jetski Engine As An Inboard

    Quote Originally Posted by StevenBauer View Post
    It was Tommy Townsend of Thomas Townsend Custom Marine Woodworking that had the lobsterboat with the jetski engine in it. It was on the cover of WoodenBoat # 198.
    Interesting. First, it's a bigger boat than I was thinking it would be, and second, this fellow did use the jet pump:


  27. #27
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    Default Re: Jetski Engine As An Inboard

    And here's the really quick and dirty version, Southeast Asian WoodenBoat:



    Like a dirt bike on water!

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    Default Re: Jetski Engine As An Inboard

    I've always thought those little longtail boats are pretty neat.

    (OSHA would love the way they start them with the props in the air. )

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    Default Re: Jetski Engine As An Inboard

    Quote Originally Posted by nedL View Post
    I've always thought those little longtail boats are pretty neat.

    (OSHA would love the way they start them with the props in the air. )
    Not to mention the "OSHA approved" gasoline containers and tanks. The real impressive ones used a 4 cylinder engine balanced maybe on something like a trailer hitch. Some of the small APBA hydros are started the same way, up on saw horses and shoved off with pilot in place.
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    Default Re: Jetski Engine As An Inboard

    Here's more "stuff" on my quest for an inboard engine for the 14'3" X 4'9" "Slippery" step bottom hydroplane that I shall begin lofting on 10/1/17. Mr. Hacker specified 40 hp for this little boat......consider the 40 hp Kohler CH1000-2012 AIR COOLED Mudboat engine of 61 cubic inches displacement and 3600 rpm max. The engine compartment is 45 cubic feet.....Jabsco makes a 12 VDC bilge blower producing 250 cfm. At 3600 rpm, the engine generates a volume of 219,000 cubic inches per minute or 127 cubic feet per minute so someone tell me what's wrong with running this engine with the Jabsco device installed pulling air out of the compartment as it enters the compartment through a pair of large Hacker clam shell vents as given to me by Mr. Bill Morgan, former owner (now deceased) of Hacker Boat Co. several years ago.
    The mass of men lead lives of quiet desperation......Thoreau

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