wave runner on a stern arch

[Pelagic]

Originally Posted by GreatKetch

Let's see...
Pelegic, do you seriously think hanging 1200 lbs off the stern of a 30,000 lb boat wouldn't be a "big issue"? Really?

It doesn't take much knowledge of boat design to know that that would seriously impact seakeeping ability.

Remember, all internet advice is worth less than what you pay for it (even mine!)

All I suggested is that he do some tests on TPCI and get some structural advice on securing before giving up on the idea, right at the concept stage.

A fat bottomed cruising boat might handle a wave runner quite easily and since we don’t know how much reserve floatation he has….hence the test.

Actually Greatketch, I get paid quite a lot of money for giving such advice about boat and ship systems from an operational standpoint, managing the feasibility study before committing.

The first thing you learn is that there are no bad ideas.….only bad solutions.

Buzzing around a deserted atoll on a wave runner is a lot of fun….and a great idea ....if he can manage the issues.

[GordMay]

Originally Posted by Pelagic

... Buzzing around a deserted atoll on a wave runner is a lot of fun….and a great idea ....if he can manage the issues.

With proviso that, the above-mentioned "deserted" atoll, should have been deserted prior to his arrival, not because of his "buzzing around".

[Reality Check]

A growing number of locations ban jet ski use and even presents... BVI has had them baned for years. Would be interesting to see what would occur if you came in with one hanging on a boat... not that they would probably ever look. However the Marine Patrol boats probably would give you some problems if they see you.

[jzk]

Why not store the jet ski on the deck near the mast? Just use a halyard and some kind of sling to launch and retreive it.

[malovich]

or maybe the best of both worlds, buy a fiberglass-bottomed RIB and graft in the guts of a jet ski to the hull. A Kawasaki 550sx can be had cheaply (see ebay auction 260290049144). Instead of a wheel or handlebar you could just have a joy-stick for steering and a simple trigger for throttle. Only problem is there is no reverse but most jet-skis can turn around in their own length.

[Ex-Calif]

Some crazy people put helicopters on the back of their boats. I told Bob to center it and lash it to the mast but would he listen? Nooooo! Right on the back of the boat.

Bobs way to smart to listen to me... I'm waiting for the boat to pitchpole. Then I'm gonna give him a big I told ya so...

[Amgine]

Originally Posted by GreatKetch

NO! That does not work. Adding weight to both the bow and the stern of a sailboat (or any boat for that matter) might keep it on a level water line, but you greatly increase the rotational momentum of the boat as it pitches in waves. The result of this is to greatly increase the amount of up and down pitching of the bow in heavy seas.

Weight belongs near the center of a boat, NOT near the ends.

Through the 50s, 60s, and 70s the argument about distributed vs concentrated ballast raged, and the net result - that concentrated is better - is correct, but for exactly the opposite reason you mention GreatKetch.

Distributed ballast results in lower rotational momentum, but greater rotational inertia. So, the boat is wetter, goes through the wave rather than over, then continues its pitch (or roll, or yaw) after the force is removed.

The whippy, increased momentum of concentrated ballast is faster, drier, and more likely to give the crew the heaves.