Two Boats In One!

Okay, the idea came from the wave runner jet ski that clamps into the stern of a larger boat, a 20 footer in fact, the ski drives the larger boat!

Now let's say I have a small 14 foot aluminum deep V boat (I do) so why can't that boat fit in the open stern of a larger boat, like PAR's Chiusa river cruiser?

Displacement speeds only, 15/25 HP OB, and trolling motors.

The small boat has the V bow but runs to a fairly flat bottom half way back, seems the "connection" area would be about 7 feet.

The beam is 58 inches midway and tapers to 48 inches at the stern.

Sides are about 20/22 inches.

Seems the mother ship could have another foot on each side, keeping the mother ship's beam about 7 feet.

I'm thinking the aft of the small boat could protrude 4 to 6/7 feet, and the surface would act a bit like a stepped bottom......or it could fit level.

The aft deck of the mother ship could be above the smaller boat as well.

The advantage is that I'd have one power plant, pushing both boats, at anchor remove the small boat and run around, zipping around, getting into shallows, something the mother ship can't do. I'd have a small planning boat and a displacement speed cruiser, all in one.

While I've spent much of the day searching for this arrangement, all I have found are jet skis and some of those run 13/14 feet. Those mother ships are planing hulls as well and they move along at an apparently pretty good speed.

Seems logical to me.

I'm thinking of a mono hull, perhaps a cat with a "center" hull might be better.

Purpose, river cruising, ICW capable, lakes and canals under 15 mph, more like 6 most of the time.

Your thoughts, suggestions :?:

 

Build it, let's see how long you use it.

Sounds difficult to keep on a trailer.

How are you going to attach the pusher to the "mothership"?

How are you going to control the pusher?

 

That's where your ideas come into play!

I'm sure we can think of several locking devices.

Remote helm stations?

You think it would be harder to tow than a 26 footer? I would think the small boat would lock in and follow the larger with a winch onto the rollers adjusted on the trailer, don't know, I've never done it, but the jet skis ride along.

What are your thoughts as to solutions?

 

BTW. I think I need to beef up the keel of the small boat as well. perhaps the gunnels as well.

 

These already exist, the front section is an inflatable
http://www.dockitjet.com/

and there are others, got there by google, jet ski pushing an inflatable, but there are others, a rigid hull

 

Hi Barry, thanks for the link.

These jet ski holster boats are what inspired the question.

Of the various boats, mostly RIBs or sport boats, they are all powered by a jet ski.

We aren't using a jet ski, we are attempting to use an 14' aluminum boat to push a cruiser, like PAR's Chiusa, it's a >26' river boat to cruise at displacement speeds.

I sure wish I could post pics or drawings, everyone likes them including me, but I can't, so I'm sorry about that. Hopefully folks can get the idea of a small power boat fitting in the aft of a longer cruising cabin/platform boat.

As practical as I see this concept, I've not seen anything like this.

The "mother ship" would have to be built. I selected PAR's Chiusa for the forward pilothouse with room aft to accept the power boat, but it could be almost anything I suppose.

I'd also say my aluminum boat weighs less than a large jet ski and it's about the same overall size, a bit more beam.

2 cross beams over the gunnels of the power boat can bolt the two together, a latch or pin at the bow plate to the sole and two (or one) "locking bar" can secure the power boat at the stern into it's berthing station for a tight fit.

Controls and steering would need to be connected and disconnected. Must have a forward helm since you couldn't see much sitting in the powered boat.

Taking the ideas of the jet ski locking into place I don't see the mechanics of this being that difficult.

The question goes more to the hull design of the mother ship, long and narrow, shallow draft or that can be beached, efficient and stable. This almost says a barge, or dory?

It must be go on a trailer under 8' in width.

This isn't going to the Bahamas, but Florida islands could be in the plans.

We've been through the design spiral and ended up with PAR's river cruisers, but can we fit this in?

 

I would suspect in flat water, the hook up from the pusher would not be easy to design. But in rough water the bow of the boat and the stern of the pushed boat will be a little harder to control

 

Very good point!

I envisioned the hook-up on still waters, about what it's like at a dock going into a slip.

Running along rivers and lakes, the mate up will probably be in no wake zones, along side a dock or with the larger boat beached.

When the boats are launched, they are already connected, so there should be no issue.

Unless there was some emergency on the larger boat, I don't think attempting to disconnect and going for any joy ride in rough waters would be a good idea at all.

However, conditions change, if you were anchored out while you went ashore, you could come back to worse conditions. I suppose if conditions were too bad, then stay ashore and wait.

Watching the jet ski hook up to the holster boats, the "slip" is pretty tight, the sides have a hard padded bumper the jet ski fits into. Several years ago I saw a Sea Do set up at a nearby lake, the jet ski almost rams itself into the opening. The bottom of the holster boat allows the bow to "climb" up into the secured position. Then the jet ski is clamped into position and off you go.

I'm not using a jet ski, but a small V fishing boat that has little rocker.

The aft end of the pusher might trail behind 4 to 6 feet, most of the pusher would be inside the mother ship.

Let's say the bottom of the mother ship is flat. In the open aft hull, on the upper side of the bottom inside the boat there can be a slight rail or built up are formed to accept the hull of the pusher boat. This rise can't be too much or it would angle the stern of the pusher boat down. I'd rather see this aft end remain level, flush or closely to the lines of the bottom of the mother ship.

I can see two ways to hook the boat in, drive it in as the jet skis do or hook a line on the pusher boat and winch it in.

As we all know, waves and wakes increase in height as they come ashore, trying to put a small (or larger) boat on a trailer at a ramp where the ramp points to open water with traffic can be a chore. I've had this experience many times, but that is on a trailer.

Yes, hooking in will take a bit of skill and timing, but going into a tight fitting slip should be much easier than an open trailer. I mentioned or suggested, two cross beams that the pusher boat would fit under.

So, I'm thinking of a hook up procedure, ram or winch in, hook the bow line strap if not winched in. Close the back gate and lock in place. Then attach the sides of the pusher boat under the two cross beams, 4 bolting positions on each side. These could be U bolts to a plate on the pusher boat, more slots than holes allows easier alignment. Crank it up tight. Now, we could also go back to that bow strap and have a hinged attachment to the bow plate. I don't see that pusher boat going anywhere but behind and inside of the mother ship.

If the entire boat was put on a sling and raised, the pusher boat's bow would be resting on rails or the bottom of the mother ship and bow attached, the sides would be bolted to the cross beams and the aft is locked in holding the pusher in place into a tightly fitted slip, the small boat would simply hang in there as a part of the larger boat. At least, that's how I see it.

Above those cross beams an upper deck could fold down over the pusher boat, it would be nice to have that as an open aft deck.

I'd like to see all this accomplished, connecting or disconnecting in under 5 minutes, I think that's possible. With better engineering of the locking mechanisms that time could be cut down.

Now, the question still remains, what is the mother ship's hull to be to allow for this aft slip with the bottoms of the two boats being in line of design for displacement speeds?

:?:

 

Back in the late 90's there were several companies developing the boats that use a PWC as a pusher. They contacted us at the USCG about this so they could make sure all was in compliance with regulations. Part of the problem is jet skis have various exemptions from regs. But your boat wouldn' t have that problem.

Anyway, their biggest problem was controls. How to hook up the controls on the pusher to the helm on the bigger boat, how to supply fuel to the engine from a tank on the big boat, how to charge the bigger boats batteries, and what lights to display at night. Lights become an issue because there is a question. Are you a barge being pushed by a boat or are you just one big boat? Anyway these are a few of the issues that have to be resolved. It's not as simple as just nosing up to the big boat and pushing it.

 

Thanks Ike, those are excellent details to consider.

So far I have assumed;

Fuel cans, one hooked up in the smaller boat, another may be stored.

A small gen set for the batteries, 1KW should do it.

Hooking up a remote helm, I don't have a clue! Steering isn't an issue, cables can be snapped on pretty easily, throttle controls, however I have no clue!

Lights, or what to call this arrangement, I'd default to the most restrictive requirement, probably two boats, two registrations. Lights of the bigger boat would be for a power boat, oh, I'll have plenty of lights for the rivers.

The pusher won't have lights on inside the bigger boat, it won't be seen, only when it's out being used.

Now, that brings up a good design point, should the pusher boat boat be all the way inside the of the bigger boat? Perhaps it should be!

That might be much better, out of sight out of mind. Don't get me wrong, I'm a compliant type, but why wave at a parked cop pointing a radar gun while you're speeding?

It seems that the big boat's bottom needs go go all the way back to the transom, while you might drive into the bigger hull, winching it in seems more prudent to me.

Come to think of it, might have some canvas that snaps on the back down just above the water line, this could keep water from washing into the smaller boat and fit around the transom. Going stealth is probably a good idea.

Back to controls, I don't think I'll try some fly by wire computerized system on a 25 HP OB! I really like the KISS approach.

That may mean I need an aft cabin instead.

If the controls have a few extra feet of cable, the same unit can be disconnected from the small boat and placed higher up for an elevated aft helm. It's starting to look more like a landing craft or a tiny tanker, or, Lord help me, a shanty houseboat. Looks matter, even if it looks like a work boat.

BTW, insurance, the small boat is insured, I doubt the big one could be being wood, at least agents in my area don't insure wood boats. Does that mean it should be a barge?

So, how do we get there from here?