# thinking about building a jet boat



## BCOWANWHEELS (Sep 25, 2013)

well been rescherching a boat build. here's what i want
engine will be either a 3.0 mercruser or 250 chevy 6 cyl, 4 cyl is 140 hp stock,6 cyl is hopped up so hp is somewhere between 175 and 200 hp
jet drive is berkley ( found a good deal on 1)
hull will be 16 ft,bottom will be .250 thick,sides .125 thick. (its rocky where I want to fish)
boat will be inboard. 
9-12 degree "v" bottom.

the aluminum isnt a problem as my supplier just told me when I want it all delivered from alcoa 5052 marine grade
welding isnt a problem as I will do it myself and I have a plasma cutter to cut it. I have spool gun and tig machines.
any thoughts ? I think I can bring the boat into being for about 4-6k. I want a completely open floor plan, no extras to try to keep weight as low as possible seeings the hull thickness is going to add some weight. also a local shop can bend the "v" bottom for me no problem.
bob


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## Ranchero50 (Sep 26, 2013)

I wouldn't run an iron engine in a jet boat that you expect to run through skinny water. I think you could easily get the performance of a I6 out of a jetski powerplant.

.250" bottom? Aluminum grabs rocks, put a 3/4" skin of UHMW on the hull and it'll slide over them.

I'd aim to have a 3/4" UHMW skinned 16' x 60" hull that weighs under 700lbs empty.

I'm at 600lbs without poly with an 85hp powerplant that weighs 80 lbs.


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## PSG-1 (Sep 26, 2013)

+1 on the UHMW. If I ever build another jetboat for myself, it WILL incorporate UHMW panels. This gives protection from rocks, without having to go with a very heavy hull thickness.


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## BCOWANWHEELS (Sep 26, 2013)

all the jet ski stuff is too expensive and it taxes the system to much to operate also the 2 cycle engines suck the gas and parts are very high. if you build a jet boat use boat stuff IMO. I want a 1/4" thick hull, it isnt that much more weight than the .190 production boat hulls.


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## RivrLivn (Sep 26, 2013)

I think all the guys were recommending with the PWC powerplant is a good power to weight ratio. By far the best is the Mercury Sportjet as a complete package and compact size for a small jet boat. Most iron block 6 and 4 cylinder engines just don't give a respectable performance in the power to weight that the others do. Some have been using the NA and Supercharged aluminum block ecotecs with some success: https://www.ecotecmarine.co.nz/ 

If people really liked the old iron 4 and 6 cylinder engines in jet boats the companies would make them; and they don't.

I run a big aluminum jet with a .250 bottom and .190 sides and I have run through 4 inches and slid across less, but I sure wouldn't want to get that thing stuck!!!


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## Ranchero50 (Sep 26, 2013)

Well, if you are going to build a tank, put some wheels on it or a winch. Heavy boats don't move well when grounded. Search Snyder boats in PA.

The ski stuff works well for me and my area and honestly was very inexpensive to buy ($1k rebuilt engine, pump, carbs), maintain ($5 in plugs yearly) and run (10mpg at 45mph). 

Where are you going to be running your boat?


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## PSG-1 (Sep 26, 2013)

[url=https://www.tinboats.net/forum/viewtopic.php?p=330494#p330494 said:


> BCOWANWHEELS » Today, 12:12[/url]"]all the jet ski stuff is too expensive and it taxes the system to much to operate also the 2 cycle engines suck the gas and parts are very high. if you build a jet boat use boat stuff IMO. I want a 1/4" thick hull, it isnt that much more weight than the .190 production boat hulls.




When I re-did my jetboat with the 4 stroke, I used an engine out of a 23 ft Yamaha jetboat, the FXHO. I agree about the 2 stroke being underpowered, especially if you are moving a lot of weight. With my boat being as wide and heavy as it is, the 1000 cc Tigershark engine just wasn't enough, it was being over-worked. But the 4 stroke has MORE than enough power, even for my 1100 lb boat.


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## BCOWANWHEELS (Sep 26, 2013)

uhmw (1/4" thick) and .250 bottom will do fine and the iron block 3.0 and its big brother the 6 arnt that heavy,about the same as a big hp outboard jet plus I already have them both, I also might install a aluminum headed sbc if weight is equal to the chevy 6 . the 6 cyl is modded pretty much. heres some pictures of my cyl head, most likely its the engine I will use, the head is pretty much maxed out perf wise, lump ports arnt installed in these pic,s but I have them.


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