Mokai jet boats

[alaskamokaiman]

So any ideas on a different motor for this boat? Another 5-10 miles an hour would be great.

Would like to keep the weight of the motor down but increase torque.

[marshmat]

This boat? http://www.mokai.com/products.html
An extra 10 mph would require considerably more power and I'm not sure you'd really want to go that fast in this boat.... and it doesn't look like its engine bay can handle much more than it has. All engines of that configuration and power weigh roughly the same, I doubt you'll find something significantly stronger that weighs no more than the Honda 6hp.

[RAWRF]

Kawasaki Jet Ski 300cc engine, couldn't weigh much.

[tri - star]

If you check out SUCCESSFUL jet boats, from jet skis
- to 400 ft long, 35 knot, catamaran ferries - you will
come to see that they all have one thing in common.

They ALL are FINITE designs.
That is: designers and engineers have spent many hours
deciding precisly what engine - what hp - and what hull
will work well together. Significant upgrades in power
will ALWAYS require a significantly, larger jet.
i.e. More expensive.
Because, ALL jets presently in use have a " sweet spot ",
where they will be MORE efficient than a prop.

Unfortuneately, above and below, this narrow range,
efficiency drops off.

Props, being inherently more primitive, are not nearly
so fussy. So amateurs can switch props and engines
around - willy nilly. And within pretty wide margins they
will still push the boat along.

Not so - with jet drives.
Unless you want to hire someone who understands
the engineering involved, you can end up with an
expensive mess. Both will cost more than the vessel
in question.

It's simple. If you want to go faster with a jet.
Buy a faster jet boat.

[RAWRF]

I have to disagree with all of the above, as do aftermarket impeller and engine performance manufacturers. The things you can do to tinker with a jet drive to make it go faster or have more torque are varied and many. No disrespect intended, and I am not going to get into details, but there are lots of things you can do to upgrade a stock jet unit/pump/engine/impeller setup.

[tri - star]

To RAWRF:
First, also with respect - let us be clear - I am somewhat
of a fan of jets.
Even had an article, that I wrote, published on:
The ADVANTAGES of jet drives OVER props.

However, I get a little testy, when people - without your
experience - start fantasizing about " improving" their
jet boat.......

Please; take a closer look at the specs of the wee, little
duck boat being considered.

As follows:
- $ 3,450.
- Molded Polyethylene
- 6 hp - Proprietry Honda Engine/Jet
- 15 mph TOP speed

REQUIRED to go: 10 mph faster.

So:
- How much cost - is reasonable to add - to acheive this
speed over the retail value ?
- When is the last time you have worked with Poly ?
Were the results, an aesthetic or practicle success ?
As shoehorning in a bigger drive train might require some
interesting mods.
- How willing is Honda going to be, to supply parts to
" improve" their proprietry unit(s) ? Will installation of,
aftermarket parts void the warrentry ?

- Finaly; given the hp available and the present top
speed..........
Consider: what is required to make a 25 ft jet boat
- get an equivillent increase in velocity.
Say from a max. of 50 knots to 75 max ?!

Therefore: I humbly suggest, that putting in a upgraded
impeller, if you can get one that fits, will not be enough.

.....Never said what is suggested.....couldn't be done.
Just to consider: is it economicaly reasonable?
As..... from my point of view - it's going to go well
beyond, just " tinkering ".

But, hey - what do I know.....?
You and alaskamokaiman, apparetly live in the same state.
So why don't you guys - get together and find a
workable solution ?

[tri - star]

OOOPS ...!!

There is a typo in the previous post.

The line that states:
".....a max. of 50 knots to 75 max !?"

Should read as:
.....a max. of 45 knots to 75 max !?

- Even I....are wanting...in precision.

Cheers !

[RAWRF]

"- Even I....are wanting...in precision."


Like a lot of other people on here, you are obviously a genius. Who cares if Honda doesn't warranty that little engine, he paid too much for that whole setup anyway, its a $500 dollar kayak with a 350 dollar engine and a 200 dollar jet unit. And if someone wants to go faster than what a manufacturer recommends, who cares? You act like this is brain surgery or something rather than the Jethro engineering it really is. When I wanted something like this, I bought a Yamaha 700cc Superjet engine, jet unit/pump/intake, etc and just stuck it in a canoe, I certainly never considered hiring an engineer or consulting anyone about it, and it worked fine. I would be willing to bet that he could put up to a 12 hp engine in that thing and have a lot better performance, as long as it fit in the engine compartment. Obviously, a company is not going to make something like that go 25mph, they would get sued because of all the idiots out there who would try crazy turns at high speed and get instantly swamped, but I know that thing could go faster without spending an arm and a leg or hiring a professional jet boat engineer.

[alaskamokaiman]

I don't want to start an angry thread....I just ask for some advise as to how to. If you are a fan of the fan explain what pitch would do in my quest.

A bigger motor more than doubles the engine weight.

Most motors run a 3600 rpm so I don't see how more horses help when you still are turning the impeller at the same rpm.

I tried the canoe thing they become very unstable with speed and turning is a whole subject to it's self.

[tri - star]

To RAWF:

I AGREE with a lot of what you say......
....'specialy the part about; ".....you are obviously a genius."

Also it's interesting that; in your statement,
"......all the idiots...would try crazy turns at high speed...swamped."
- You seem to agree with me - that hopping up this boat might
not be wisest thing to do.......

Also it seems; you concur with marshmat.
Who said,
".....not sure...want to go that fast in this boat."

...................................

To alaskamokiman:

In the interest of reason and helping you out a bit,
I will make a few suggestions.

If you go to the DESIGN sub forum here - you will find
- TWO PAGES devoted to " Jet Drives ".
Within the first page, I'd check out, in particular:
" Jet, Jet pump........" by brian eiland.

By you statement,
"....I don't see how more horses help when you still are
turning the impeller at the same rpm."
- You are beginning to see that, as I've suggested, that
making alterations to jet drive trains: IS more complicated
than changing props is.

As with a prop, changing the GEOMETRY of the impeller
will change the performance of a boat. In similer ways.

Going faster with what you have is the easiest.
i.e.
With more hp, the MASS ( the weight in water ) can not
increase, at the same rpm - with the SAME DIAMETER impeller.

However, with more hp, you can move said, MASS - at a
FASTER rate.
This follows the basic Newtonian rule:
- That the SPEED of a jet boat is a function of how FAST
the water is leaving out the back of the boat. Combined
with the amount of MASS.

So an impeller, designed for a faster movement of the water
- though the jet - will make the boat go qucker.

Getting more bottem end is more difficult... if you also
want to keep the higher top speed....

Without the unit, on the workbench. In front of me.
I would hesitate, to suggest as to what impeller / jet / engine
combination, will achieve your objectives.

Also, considering ALL the above, I'm most likely to - refuse to
advise you to do - much of anything anyway.
- And I'd definately refuse to take any MONEY from you.
As I cetainly don't want to be responsible for your early demise,
or the inherent legal liabilities involved........

Cheers !

[klondikejim]

Having just purchased a few Mokai's, and only going out on them once, I am not the formost authority on them, but man, I got drenched on quite calm seas. I can imagine how wet I would get if I were to go even faster. Heh. Great little toys though, cant wait to accessorize it for the hunting/fishing season to come.

[kengrome]

I have emailed them many times and they have never replied, so I figured they are no longer in business. Good thing to know it's a wet boat though, thanks for that info!

[klondikejim]

Wierd, in all my dealings with MOKAI thus far, they have been pretty customer service oriented. I know they are a small business though, so perhaps a bit busy is more the case.

[alaskamokaiman]

Am really surprised that you have had a problem getting in contact they are great with customer service.

They have the new web site up try contact again "mokai.com" If you don't get a response send me your contact and I will get them in touch with you.

You do get wet when you play in chop and waves the spray skirt works will, a rain coat keeps top side dry. We need to make a small dome for cover when in bad weather.

I have had mine for 4 years and love them as much if not more than when I got them not a boat for everything but will get you where no other boat can follow.

[kengrome]

I've emailed them numerous times from three different email addresses but they have always ignored me. When a company publishes an email address on their business web site, isn't it logical to expect them to respond?