Looking for pros and cons of building an aluminum jet boat

[sms986]

I have been in desperate need of a new boat for a long time. I have an '87 duracraft jon with a with a '63 40hp evinrude on the back. The boat is SMALL.

I want to finally buy something that I will not have to worry about fixing something on or getting stranded on for a very long time. However, new boats are insanely expensive. What's better is that some people think the value goes up after they've used them for a year.

so I decided to save money and build myself a boat. I want an aluminum boat, because I fish a lot of shallow rocky areas. I also want plenty of room so I never fall off again. Last, I don't need to break the sound barrier. I'll be thrilled to have a boat that goes 50 max.

Here's what I've come up with. I'm going to order a custom made aluminum 2272 boat and put two '98 yamaha gp1200 engines on the back. I've got a few questions and want to hear pros and cons.

First, I do want to say that I'm using the two yamaha motors because I want a jet drive for shallow river running. I know that they are '98 models but I really like the yamaha two strokes. In fact, I have a gp1200 jet ski now from '98 that has never been rebuilt/tinkered with/repaired. It runs like a top. I also got a great deal-unbeatable by a comparable outboard on the donar skis.

Now I know that two 135 hp jet ski engines sounds like overkill, but if you factor in the 70% power loss with a jet drive, they're 90hp each. If a 40hp can only push my 15' jon 25 mph bare naked, I doubt the single engine will be any better on a 22' loaded down with my gear. Second, I don't drive like a maniac. I'll probably only be top speeding to get up rapids and on long straight stretches. And last, if I have two engines, I can run miles up into the wild and not worry about getting stranded (unless I'm double unlucky).

So the only question I have right now is if a flat bottom mod vee would handle ok at 50, or if I should go with an 8 degree vee. The flat bottom has strakes, the vee does not.

I also want to hear your opinions and pros/cons.

Thanks!

 

[BWR1953]

I thought that a jet was only a 30% reduction in power compared to a prop, not 70%.

 

[Chris1956]

So you are looking at a V hull Jon boat, made for an outboard, but you are gonna install twin Waverunner motors, with their twin exhaust systems, wet mufflers etc??

Why not a single jet outboard? It will be a lot easier to make work...simply bolt it on and go.

 

[sms986]

I thought that a jet was only a 30% reduction in power compared to a prop, not 70%.

Yeah I wrote that backward but you know what I mean! Been a long day...

 

[sms986]

So you are looking at a V hull Jon boat, made for an outboard, but you are gonna install twin Waverunner motors, with their twin exhaust systems, wet mufflers etc??

Why not a single jet outboard? It will be a lot easier to make work...simply bolt it on and go.

A single 100, 150, or 200 hp outboard hanging off the back would raise the bow much more and make it more unstable than two inboards at higher speeds.

Many other reasons I don't want an outboard, but the biggest is I have two running skis for $1200. With that money maybe I could afford a 20hp jet from the 80s. Outboards are expensive! If you know of a 100-150 hp jet drive outboard for a reasonable (maybe $3k) cost, please let me know (I'm serious, I'd give it a look).

 

[Scott Danforth]

nothing wrong with an aluminum jet boat

 

[BWR1953]

Yeah I wrote that backward but you know what I mean! Been a long day...

Whew! I'm just glad that I'm not as senile as I thought I was! :lol:

 

[Chris1956]

Of course, most outboards from the mid 90s can be converted to jet drive, or bought used that way. No one wants those 2 strokers from that era, so they will be cheap.

An outboard will allow much more room in the boat.

"A single 100, 150, or 200 hp outboard hanging off the back would raise the bow much more and make it more unstable than two inboards at higher speeds."

Exactly how did you arrive at this conclusion? Bowrise is a function of the hull, not the type of powerplant. At least you can control the trim of an outboard. Also, If you plan to overpower the boat, than any kind of powerplant could make the boat unstable.

I still don't understand the advantages you the boat you propose...

 

[sms986]

Ok.. I will explain in detail the advantages of an inboard powerplant (like I am proposing) versus an outboard. I don't want to get into an argument over this. I've always admired the folks on this forum for generally having constructive and respectful conversation.

The first simple advantage-cost. The engines, along with pumps, most of the controls, gauges, everything, will cost me around $1500 end of the day (after everything I don't need gets sold). In my research, it would be even more money to buy an outboard and convert it to a jet than to simply buy an outboard jet. Then I need to buy all of the controls!

Second advantage- if one breaks down, I can at least get the boat home on the other (I really like this one).

Third advantage-nothing hanging off the back for me to tangle in if a fish runs to the back or if I am trolling. I always get wrapped around my o/b. Sure I can get tangled in the jets, but they are overall an astronomically smaller obstacle.

Fourth advantage-ease of simple repair on the water. I plan on having an access deck that can be flipped totally over on the transom side to access the engines. This also means the whole 22' of the boat can be walked across, as with outboards. As far as layout of deck space and storage, I think it's perfect. I have all the room I want and more.

Fifth advantage-trim has never been as much of a dialed in process on any jet boat I've ever been on-none of them ever needed trimmed. A boat shop guy I once talked to said jet boats, in general, are much less dependant on trim for performance than prop driven. Most don't even need it. However, you can adjust the nozzle angle on the Yamahas, which is trimming them. I also like the option of being able to adjust the side to side tilt that's offered with two jets. If one side gets heavy, I can adjust just that one nozzle angle down slightly.

Sixth advantage-weight distribution. The position of the powerplant most certainly affects bow height at low speed, high speed, and no speed at all. It's simple physics. If I have a bulk of the gross weight of the boat hanging off the very back, PAST the aft end of the bouyant length of the boat, that will positively naturally raise the bow much higher than having that same weight about 80% downlength the bow of the boat, INSIDE the bouyant domain of the boat. That's simple physics. Kind of like if you overload the bed of a pickup. Now imagine having that same weight hanging off the outside of the tailgate! Outboards are NOT light. I remember in Canada we would rent 15' vee hulls with 25's on the back. We had to load the bow with rocks just to keep it down.

Seventh advantage-stability at moderate to high speed, in conjunction with the above statement. I think it'll be much easier to flip the boat with all the weight on the very back as opposed to being inside the hull, 2 feet further up toward the bow. By flipping, I mean bow over stern upside down.

Advantages I can see from an outboard-like you said, simple clamp on installation (I do like this one).

Potentially better fuel economy (the ski engines are thirsty.

Simplicity of repairs (hanging off the back on a trailer, out of the water)

I posted this topic for this reason. I want to explain my pros and cons and see the differing opinions to make a good decision overall.

 

[Scott Danforth]

first, take your budget and multiply by 4, take your time estimate and multiply by 5 or 6

 

[sms986]

I think I'm good on the budget. Got an exact price on the big stuff and a quote for the hull. Tripled the rest.

 

[Chris1956]

Sounds like you have all the pros and cons figured out. Good luck with your project.

 

[DeepCMark58A]

If you are using a jon boat and a jet drive because of shallow water going 50 mph is not the best idea. Matter of fact the only worse decision would be going 50 mph in the dark.

 

[sms986]

Most of the time I'll be in deep water. I do want the ability to run shallow though, for which I won't be going that fast.