drive for landing craft used on both ocean and rivers

jet drives are about the only working solution for rivers/creeks.
A landing craft isn't the best solution for the ocean, but that is what is needed for off loading small vehicles, such as an ATV. Props are great for the ocean, but not for near the shore.
Outboard jet drives claim the solution, but how about efficiency?

So let's start with the boat...24' to 26 landing craft, aluminum, full cabin side to side located fairly
close to the stern. Some solar panels for charging batteries up top. Anchors for each end to load/
unload on the shore. UHMW on the bottom, forward to prevent wear by sand and rocks. Wheel
house raised above the cabin for viewing over the gate and to see river rocks. Controls so the
operator can run everything solo. 1500 pounds max. load except for fuel. I'd prefer to be able to
go 700 nm in 3 days on the ocean loaded (230nm/day). With a 12 hour day that's about 20nm/hr.
I'm guessing that the boat would have to be planing. If I fill with fuel twice on the trip, then I'm
guessing about 12 gallons per hour x 12 hours = 144 gallons, plus to make sure I'd have enough.
So, maybe 200 gallons of fuel. Dry boat weight is about 5800 pounds. I've been told that a
Hamilton 241 jet drive would be about the best drive. When I ran jet boats on the Salmon river in
Idaho, we used 460 c.i. engines. But that was about 45 years ago. We had problems with sand/silt
wearing the jet drives. As they wore, we would have to run the engines at higher RPMs.

 

HJ 241 hamilton jet best suited engine option. Old thread
Not sure if the information will help

 

Your link didn't link, Barry. This should work:
HJ 241 hamilton jet best suited engine option. https://www.boatdesign.net/threads/hj-241-hamilton-jet-best-suited-engine-option.63425/

 

Hi richinname, sand and silt are minor problems for jets, stones and pebbles are worse, damaging props and wear rings, mostly happening when powering up to drive in on landing, and when leaving. At least a prop in a tunnel is less likely to accumulate stones, and much easier to inspect and replace the prop. if damaged.

 

It's not going to work with a boat that small. You won't get the range. Also, landing craft are not very seakindly. I worked on them for diving, and would not like to be offshore in any kind of weather.

 

Actually, a hovercraft offer options that will support almost all his requirements. All-weather open ocean would be a bit of a challenge, but it would be the same for a jet drive on something that small.

 

In my opinion if a river is shallow enough to to warrant jet drives the ATV can just drive trough it.
Anyway, I don't see why he can't have both, props and jets. Two propeller outboards on the transom and a jet in the middle. Use the props as long as possible then pivot them up and continue with the jet.
I don't know anything about the operating conditions or route but there are options to minimize the additional weight, for example on a regular route he could unship the jet once out of the shallows, or he could use a much smaller jet engine going slow in the shallows, or he could have a single inboard engine powering both jet and prop, put a foam core cabin on the Al hull, etc.

 

About Us https://www.abeltasmanseashuttles.co.nz/about-us/

You can hunt around on this site for other informaion. Many years ago I rode on two of their larger shuttle vessels. One had drives similar to an I/O but when the boat came close to shore the
leg could be rotated around the input shaft to the leg. . This would them move the prop up close to out of the water to allow beaching
The other had twin 300hp Scania Diesels. The diesel was mounted above drives and the output shaft of the diesel had a set of pulleys, with a number of belts to drive the shaft for direct drives.
The leg and diesel were mounted on a vertically movable pod so that as the boat came in, the engines and props etc moved vertically upward and the prop was only partially immersed.

They did show a video on the boat and I and others have tried to get a copy, but they did not respond.

You need to perhaps specify the water depth that you want to run in the rivers and the depth at the transom when you are beaching the boat. A landing craft trying to minimize draft for a river
might need a 6 to 10 degree deadrise. Fine for small waves generated on a river. But for an ocean this deadrise will be bone jarring in bigger waves.

In inboard jet would be about the best compromise with say a 12-14 degree V, still rough in big waves but ok for shallow water.
You also mention fuel efficiency, if you put this down on the list, outboard jets would also be fine. Just might need large ones for the size and weight of the boat
Certainly backing off a beach by reversing the nozzle can cause injestion of rocks into the pump. Berkely, AmericanT worst offenders, Hamilton much better.

It appears that you wishes are at opposite ends of the spectrum, ie shallow water beaching, low deadrise, and ocean running higher deadrise, assuming larger waves all the while wanting fuel efficiency

Pick what is most important, produce some depth info, and you will probably get some good ideas from this forum. Might be a good idea to put some budget numbers on the table as well.

 

700 miles of ocean in a small landing craft that needs to be able to transit shallow rivers. That's a lot of ocean in a shallow boat, going to make for some tight weather windows.

Although usually 28 to 35 feet long, prince William sound bowpickers are the closest your going to find with a similar load and ocean as well as river shallow capacity. These days almost everyone trailers for the real long hauls, but a few guys run from homer to cordova. The round trip is a little shy of 700 but close enough.

Could probably Google pws bowpicker and get an idea for designs around load carrying jet boats.

 

Nice looking boats.

They have a link on the gallery and video page:
https://www.youtube.com/user/ATSeaShuttle

A cat is not so good for very shallow areas. For shallows, a false bottom deployed with an air filled bladder between the hulls would reduce draft and turn the cat into a scow. It would reduce draft (and stability but not cost). 12 gph, 6.2 lb/gal, 0.4 lb/hp hr, ~186 hp at cruise, 20nm/hr, 25 feet, about 2 mpg. Sounds a bit optimistic. You will certainly have to keep the weight down. Maybe skip the retractable bottom and look into a side wall hovercraft. Good luck. These ideas are worth what you paid me for them unless someone else comes along who can flesh them out.

 

I just noted your location in Idaho so with an assumption that you would be using the boat in the pacific northwest, I would remove my suggestion that an inboard jet would be the best solution.
Jets can have issues injesting kelp. Plugging intakes and wrapping their tentacles around the input shaft in the intake in the pump. Extremely hard to cut out.
Perhaps an Arneson or TSD surface piercing unit might be better.

 

Good point, Barry! "Been there, got it all......"

 

One of our SES ferries operating in the Med was nicknamed "Hoover" While maneuvering in to the quay she sucked up a tire. Took four of us all night to cut the tire out of the jet....one little "snip" at a time. On another occasion, it was a large carpet or rug.

 

It is indeed a challenging SOR. While Serenity would make a better landing craft than most, and can carry the load you want at the speed you need, in shallow water or storm, the fuel consumption would be... let me see, converting. The same as you require. Okay, a manageable SOR. Twin outboards on power jackplates. Done.