chine walk or associated problems

About using jet ski motors to power small boats

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slociviccoupe
Posts: 31
Joined: Tue Jun 09, 2009 11:08 am
Location: Palm Bay Fl.

chine walk or associated problems

Post by slociviccoupe » Sun Jun 14, 2009 8:50 pm

Has anyone had problems with these small boats pushing them upwards of 70mph. Speaking of this is there chine walk with a jet drive? And what about the bow lifting at speed, any chance of blowing over or porpoising?
Im using a seadoo motor and pump in a dynojet. Plan on Extending the length to 12' even. Pump will not extend from the back of the transom but will be tucked under like it was in the ski. i know I will be overpowered. starting with a 951 seadoo motor and 155mm 10 vein pump. Motor will be a pump gas 1050cc big bore. stock motor puts out 140hp. so the big bore should definately put out more. the donor ski is capable of 70+ mph. And I would like to achieve the same performance in the boat.
another question is can the deck be constructed like the hull. .25" ply and then glassed over. Im mot a fan of the planked wood decks. And prefer to paint mine.

upspirate

Re: chine walk or associated problems

Post by upspirate » Mon Jun 15, 2009 4:05 am

Most of these hulls are designed for ply decks....the builders opt for the planked look and add it.

There's a Squirt jet that was made to resemble a mini flat bottom SK V-drive

Forgot who built it,but it's silver and blue I think,and there's a video on You-tube...search Glen-L

Any boat can blow over running that fast,just have serve your fast boat apprenticeship and take it up slowly...learn how it handles in stages.

You wouldn't put a teen in a performance car without learning basics first and then stepping up.

slociviccoupe
Posts: 31
Joined: Tue Jun 09, 2009 11:08 am
Location: Palm Bay Fl.

Re: chine walk or associated problems

Post by slociviccoupe » Mon Jun 15, 2009 4:23 am

thats 100% true. id rather have the power and be able to control it than not have enough power to get out of a situation.
My friend races 250cc outboard hydro's. He has blown over twice. he says you become a rag doll at those speeds. He is aproaching 120mph in a 10' hydro.
my question though is chine walk, do jet drive boats have this problem. I thought it was only associated with prop boats. Im still set on building the dynojet. The engine should put out a strong 200 hp on pump gas. mated to seadoo's largest and best pump with the right impeller 70 is highly achievable. especially when the new 4 stroke jet ski's weigh in at close to 700lbs.
Im hoping with the light weight of the dynojet construction and the light weight of the seadoo 2 stroke displacing 1050cc's should get me up to speed and one heck of a holeshot with no cavitation.

upspirate

Re: chine walk or associated problems

Post by upspirate » Mon Jun 15, 2009 4:41 am

I really don't have any experience with jets,Caber-Feith on here does,so maybe he'll answer or PM him.

I think the guy that had chine walking on a TNT ,which is almost flat at the transom,had it from prop torque on a small boat.

I only got that when I put an old 4 cyl Mercury 80 on my first TNT cause I had both sitting around(beer was involved!! :wink: :roll: ).

Usually you get chine walking in a deeper V hull(that's why they went to pad bottoms ).

With the Dyno-jet being a V-bottom,you could get some chine walking at higher speeds as the boat raises higher out of the water I suppose,but don't know if the jet would make a difference.

On the old Checkmate outboards in the late 60's when they chine walked,they installed tabs to stabilize this problem.although I never understood the concept,they installed them parallel to the water instead of at an angle even with the V of the bottom like they do with Bennett trim tabs

slociviccoupe
Posts: 31
Joined: Tue Jun 09, 2009 11:08 am
Location: Palm Bay Fl.

Re: chine walk or associated problems

Post by slociviccoupe » Mon Jun 15, 2009 5:07 am

hopefully the vts trim system that is on the seadoo pump will be usefull on keeping the bow down. Im planning on putting the battery and ignition boxes on the side opposite the driver to try to ballance the boat a little better. Not sure where Im going to put the tank yet. Was thinking of the possibility of trim tabs, not sure if they will be necessary.

upspirate

Re: chine walk or associated problems

Post by upspirate » Mon Jun 15, 2009 5:14 am

You know,in thinking about it (guessing here,no experience) the jet has a ride plate, and has a somewhat flat area aft,so I don't think you would get much if any chine walking.

You could always add some strakes just to the sides of the pump intake from the transom forward to where the hull turns upwards,and that may stabilize the walking tendency.

These could be added later if needed.

slociviccoupe
Posts: 31
Joined: Tue Jun 09, 2009 11:08 am
Location: Palm Bay Fl.

Re: chine walk or associated problems

Post by slociviccoupe » Mon Jun 15, 2009 5:20 am

was looking at other boat designs and the addition of chine rails is another option. Newer jet skis have chine rails in the hulls. heck my donor ski does. And yes the seadoo ski Im using as a donor has a large ride plate that is completely flat.


wwamann
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Location: Freeport Florida

Re: chine walk or associated problems

Post by wwamann » Mon Jun 15, 2009 10:21 am

upspirate wrote:You could always add some strakes just to the sides of the pump intake from the transom forward to where the hull turns upwards
I'm not sure I did this quote thing right , anyway

the strakes in this arrangement may lead to an increased chance of pump cavitation in choppy/rough water by trapping air between them and funneling it directly into the jet intake.

A well designed hull for a jet will have at least a 9-12 degree deadrise with any strakes near the intake ending 2ft to 4ft before the intake.

That way the deadrise should force any air trapped by the hull out towards the chines before it reaches the intake.

wwamann

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Caber-Feidh
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Re: chine walk or associated problems

Post by Caber-Feidh » Mon Jun 15, 2009 12:15 pm

Chine walking is very rare with waterjet drive. The rideplate, intake shoe drag, and necessary amount of wetted area to keep the intake in quiet water preclude the dynamics involved in a nice happy chine dance. The fact the thrust force is applied to the hull at a higher location (the motorboard) on an outboard allows the hull to act as a bit of a pendulum between the motor mount point, and the center of the propeller. With a jet the force is applied much lower, centering in the area between the middle of the nozzle, and the top of the suction piece.The problem of chine walking is further reduced by the fact the waterjet is traveling in a straight line, there is no twisting force in the water to work against hull stability. To the lake, the hull "appears" longer. The water stream increases the effective length of the hull relative to the volume, and velocity of the thrust column. All the water mass exiting is also entering, that weight aft, and low makes a big difference in hull balance. On a typical full size pump the volume to fill the bowl, outlet, and suction piece will be around 50 gallons. That's allot of ballast in any small hull. (a PWC pump would be less).

Ideally, the keel should make a smooth, soft, shallow arc through the back 1/3 of the hull. Strakes should be at least the width of the intake away from the intake. (general rule of thumb). Strakes should be shallow, but are a good thing. (they are the only stability-inducing structure between the driver, and the water.

Jets kiting are rare, it's a self-limiting problem, once the nose gets too high, the pump looses the pressure of the hull on the water, and cavitates, sucks air and the thrust is gone, and it's over. Ya, it could still happen, but it would take a set of circumstances that would be unusual.

Porpoising is a far more common jet problem, and usually easy to cure with minimal hassle.

Now if you build in some strange hook, or imbalance, or have the hull loaded with a load far forward of the Cg all bets are off.


trim tabs+jet drive=eternal weirdness that makes you think it needs an exorcist.

Chine walking can add some interest to your day, are you sure you don't want it? :wink: Nothing like getting shaken out of your boat and ending up in the 45 degree water to leave you with an unforgettable day on the lake. (been there. a few times :shock: ) Makes you appreciate a good life vest that can take some thrashing and still stay on! Now the vest-burns on your neck and arms are a great conversation starter... and the hair does grow back, sooner or later.
Some plan to stroll through Saint Peter's Gates, I plan to go through them at 150mph... backwards... in a screaming ball of flame, with a glimmer belt wrapped around my head, and a NOx button in my hand.

slociviccoupe
Posts: 31
Joined: Tue Jun 09, 2009 11:08 am
Location: Palm Bay Fl.

Re: chine walk or associated problems

Post by slociviccoupe » Mon Jun 15, 2009 1:27 pm

Back In 97 I raced kawi stand up jet ski's. Getting thrown off a boat at 70mph is not very fun, and some how another rider or your own boat seems to find you, some supernatural force that you get run over by something. Ive hit the water so hard one of those racing chest protector life vests from name brand slippery when wet, I came out of the vest when I hit the water. Ive never experianced chine walk nor want to. Thats how my friend blew over once in his 250cc outboard hydro. severe chinewalk got air under the hull and at 120mph he blew over.
Very interesting info on the hull shape before the pump inlet. Im very open to suggestions before I start building my boat and find out more info later. Im just wanting to get the most out of my boat. Id really like to find a used set of plans so I can put more money into building supplies and parts for the driveline. Hopefully once I can get a set of plans I can use the lofting technique to draw the parts In Auto Cad and have them cut out on a cnc router. Has anyone ever thought of implementing tabs on these parts so they align themselves. would go together like the building blocks with the milled spots on them. Just an idea that came from experiance in production wooden kit parts. Just like building a big model.

upspirate

Re: chine walk or associated problems

Post by upspirate » Mon Jun 15, 2009 3:51 pm

Several members have used these programs for cutting the parts.

If you are going to build a production run,it may be worthwhile,but for a one-off,it may be a lot of unnecessary work(I have no experience with the cad stuff), someone else may chime in on this.

On a normal ply on frame build,there is a lot of fairing so small discrepancy's aren't a problem,not sure on a stitch and glue build

You COULD buy used plans for less money,but remember that their are a lot of people on here that have some good advice, and a lot of members have strong feelings about the one boat from one set of plans copyright mindset thing.

Glen-L has provided this forum and lots of collective experience & advice at their expense not ours,so most of us feel that we need to support Glen-L 's products where we can.

In the long run, a complete set of plans is a small portion of the overall expense!! :wink:

slociviccoupe
Posts: 31
Joined: Tue Jun 09, 2009 11:08 am
Location: Palm Bay Fl.

Re: chine walk or associated problems

Post by slociviccoupe » Mon Jun 15, 2009 4:18 pm

i agree, and Im going to bite the bullet and order my plans next week. After I put the plans in autocad and create layouts for the plywood sheets. Ill contact glen-l and see if they would want a pdf file of the cad drawings. help other fellow members out and bring some money to the site. its people like members on here and supporters that keep things going and the hobby alive. Ive got 10 years cad experiance, 3 years machining, and 2 years aircraft cunstruction. No reason to keep it to myself, share it with others.

upspirate

Re: chine walk or associated problems

Post by upspirate » Mon Jun 15, 2009 4:24 pm

Fantastic,
I was hoping you would get what I was saying & not get toes stepped on!

The tabs sound like a good idea to keep the panels in alignment while stitching.

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