Towing a spare boat??

[ted655]

I want to tow my fishing boat behind my houseboat.
I envision a 1 7/8" trailer ball sitting on a reinforced pad, mounted in the center of my bow deck on the fishing boat. A set of eyepads, one on each side of my HB stern. A towbar set up much like RVs tow their little cars hooked between. Only the hook up is reversed, the ball on the towee & and the towbar on the tower.
The fishing boat is welded plate aluminium, fixing the pad for the ball is not an issue. The hull of the HB is fiberglass, so massive 1/4" backing plates on both sides of the pad eyes would be needed there.
I see the towed boat being able to turn with the HB, as a trailer does behind a car. It can also swing up & over any wakes from other boats and of coarse the pivot action of the ball & coupler give flexable movements also. River & freshwater operation, NO ocean travel.
I see a rope tied to each side of the stern of the towed fish boat. To load into the boat, one rope is slacked & the other used to pull the stern around to the HB in a 1/2 circle.
OK, what am I missing?
HB is 42' long, fish boat is 24' long. Thamks:confused:

[FAST FRED]

Are you that bothered by waves astern tossing the towed boat into the HB?

Would assume its much more a problem if the tow is wind pushed faster than the HB.

No reason your system shouldn't work.

I prefer davits , as its easy to load & unload , no bailing after the rain , and in some areas Lots harder to pilfer the engine.

FF

[ted655]

Yeah, I can't davit a boat this size. 24' X 8', 3/116 alum plate + equipment.
My whole life I've "tied & rigged" towed boats. Usually ends up being Murpy's Law type situations. The 2 main reasons for yhis approach is, 1. Lots of locks to pass through in an organized, timely manner. 2. the HB is a sterndrive. The "dipping ropes cause no end to worry. (yes, I've seen the mooring whips solution).
One of my concerns are the large wakes from commercial tows we will pass.

[Capt. Mike]

By making your tow rig rigidly fixed to the stern of your houseboat, you will certainly reduce the manuverability of your houseboat. Of course the hb turns by swinging its stern from side to side. If you fix your tow to the stern, the lateral resistance of the fishing boat will reduce the hb stern's ability to swing and therefore its ability to steer. Generally a tow line is fixed to a point or points (in the case of a yoke) that are far enough forward of the stern to allow the towing vessel's stern to manuver.

Mike

[SamSam]

Ted,
Maybe your spare boat is too big. Couldn't you downsize and have less problems? Sam

[TerryKing]

By making your tow rig rigidly fixed to the stern of your houseboat, you will certainly reduce the manuverability of your houseboat. Of course the hb turns by swinging its stern from side to side. If you fix your tow to the stern, the lateral resistance of the fishing boat will reduce the hb stern's ability to swing and therefore its ability to steer. Generally a tow line is fixed to a point or points (in the case of a yoke) that are far enough forward of the stern to allow the towing vessel's stern to manuver.
Mike

This might not be as much of a problem as it seems.. The path the tow will take as you start to turn, is to push it's bow sideways. As soon as you do that, it will actually add some force in the same direction, I expect, like a rope-towed boat does when it heads to one side... There MAY not be a lot of force needed. Something like this must have been done before...

Or prototype it with a couple 2x4's and rope lashings??

[SamSam]

That's an idea. Do a little more rigging and turn the tow into a giant rudder. Sam

[safewalrus]

Remember on the water everything is flexible! the Houseboat (tug) moves every way possible, up, down, right, left, sideways, twists, turns bobs and generally buggers around so to does the tow! A rigid joint would fracture in seconds with all that movement (if your lucky - if not you'll rip a plate out of the deck!), which of course is why its not been done before! Use ropes they are flexible enough for the punishment you'll be giving the gear - try towing alongside - lash your fishing boat to one side of the houseboat, will give you all the control you want and need (just make sure you can go through a lock like this) Try it!!

[ted655]

Nope , I need my big boat. Crab traps, shrimp trawl, water taxi once HB is moored. Water transport, fuel & "beer".
I was thinking the ball would turn, twist, bend, rise, fall, etc.. Starting & stopping would just push or pull on the brackets. A force they should be able to handle.
I do wonder how the HB will handle in a turn? Much like a car does towing a trailer around a corner? Just playing with cardboard here at home, I DO see a "brief" push from the towed piece. But then, it also begins its turn and the push is gone. Can I count on side slip of the HB hull to dampen this push?
I have never been able to lash a boat to the side of another without some movement, AND I've never kept a fender where I put it. Alum scraping against fiberglass.... I shuder when I think of it. The fish boat has a square bow with sharp, right angle corners that would work like horns on a bull & the gunwale would get its licks in further down the side. Ya'll ain't lived untill your tow harness drops down & winds around your prop on a sterndrive.
Hey, I'm listening, and I don't disagree with some of your concerns. Rather, is there a solution to them?
Nothing is really "fixed", the ball will allow for all movements, but to a point. I'm wondering if I'd ever encounter a combination of movenent that would be the equivelent of a jackknife?
Also remember I will have a nylon rope tied off on each side of the stern of the fishboat. These will act to "mostly" keep the boats in line, yet streach in a turn.
Thanks,

[SamSam]

Say you have to stop in midstream with the current coming from behind, that would turn the tow sideways and then being so big that would put the whole works out of control it seems. Reverse anywhere would be a problem. Maybe you should push it like a barge. Sam

[ted655]

I see your point. A big rudder at 90 deg to the HB.
That is why I thought of 2 ropes tied off (port-strbd.) to the stern, to prevent that drastic a turning.
Reverse is a problem.. Hmmm? I am hesitent to push it. The HB has FLS & a true signal might be difficult to obtain with that long a boat out front.

[charmc]

One of my concerns are the large wakes from commercial tows we will pass.

I think that's precisely the problem with the towbar approach. Safewalrus mentioned that also. Murphy's law of boating says there will always be waves bigger than those you've prepared for. The wake from a commercial tow can be very powerful, and I see a real possibility of hull damage from the combination of simultaneous vertical and horizontal forces acting on a towbar. You could do as the commercial tugs do, tow your fishing boat with a nylon bridle and tow rope most of the time, and shorten up on the tow when in close quarters. You'll be going dead slow around locks and piers, so bringing the towed boat up very close should not cause any problems.

Charlie

[TerryKing]

Remember on the water everything is flexible! the Houseboat (tug) moves every way possible, up, down, right, left, sideways, twists, turns bobs and generally buggers around so to does the tow! A rigid joint would fracture in seconds with all that movement...(snip)

You're right that a rigid joint with those two large masses would break something! Still, the problem when the tow runs up your butt when you slow is difficult to handle. Going up the Chambly Canal between Lake Champlain(Vermont) and the St. Lawrence River (Canada) I have seen a few towed small boats temporarily lashed up tight to the stern, with some fenders or something. I THINK I once saw some cushion-thing that was intended for the job. But that wouldn't be good at speed!

WhatIf you had a triangular tow 'bar' like you proposed, but had a very shock-absorbing connection, like heavy 'Bungee' or mooring snubbers, allowing about a foot of relative movement in all directions??

[FAST FRED]

Interesting , that L Lord talks of towing a "trailer" if your boat is well up on the plane.

Seems he would hold the stern of the towed boat very close to the stern of the towing boat .Yes, the towed boat is stern first when towed.

A wide LB ratio was desired for the towed boat , and very little extra power is required to do this.

Is your HP fast enough? SL 3+ ?

FF

[ted655]

It's a Volvo 6 diesel, 130 hp. STERNDRIVE, the prop sticks out approx. 32" from transom.. Therein lies my concern with rope tows.
====" WhatIf you had a triangular tow 'bar' like you proposed, but had a very shock-absorbing connection, like heavy 'Bungee' or mooring snubbers, allowing about a foot of relative movement in all directions??"========
My bud, who is an old sailor, suggested just that. What we came up with is this: The A-frame, with a drawbar that is pivoted at the end of the A-frame. Back, closer to the HB, where the A-frame attaches to the HB transom, the end of the drawbar is attached by a short length of chain & a strong spring. One on each side. Adjusted to keep the drawbar centered. When a lateral force applies, the one spring/chain falls slack and the opposing set absorbs the force, pulling the drawbar back to center, the slack spring/chain raising back into position. We came up with this because we know of no "bomgee" heavy enough to do the job. We've not figured out the lengths of each end of the drawbar. How much "fulcrum" the spring end needs to be viable. Wish I were smarter, I'd know where to put the pivot bolt.
He happens to have a 4" heavywall aluminium pipe, 10' long. Looks good for the drawbar.
Thanks,
__________________

[ted655]

I.ne located some 5/8" shock cord, rated @ minimum break strength of 500#
Anyone know of any bigger?

[TerryKing]

I.ne located some 5/8" shock cord, rated @ minimum break strength of 500# Anyone know of any bigger?
Wow.. that should do it.. Thinking about the forces, the fore-aft forces shouldn't be anywhere near 500 pounds unless you suddenly go WOT or one boat or the other hits something. The Side forces from a large wake hitting from the side still don't seem too bad if the compliant shock-absorbing mount you make has some travel to it. I sort of envision a 12 to 18 inch square or circle as the outer part attached to your tow bar system, and the center attachment point on the towed boat. Maybe. You can experiment with the shock cord configuration, from one strand every 120 degrees (3 cords) to a double strand every 90 degrees or more...

But it seems, from my unscientific testing of recalling fending off medium size boats with a good hard foot-shove as they were about to the hit the dock, that something like 100 pounds (Which a good shove from a large Mariner might provide) had quite an influence on the Bow end of a small boat. And a lot less on the stern, where there's a lot more mass and resistance presented.

Heck, I don't know how to calibrate this... I'd prototype it with some lashed-together 2x4's (That's a US inches thing...) and the shock cord, first.

Make sure you let us all know how this works out, because One Of These Days I'm gonna run a boat big enough to want to tow another boat :-)

[ted655]

As for mass, the bow is as square as the stern (well... slightly tapered). There is a 5' rake on the bow. The boat draws 10"-12" deprnding on the load. There is the OB shaft & skeg at the stern. I'm thinking of making 2-4 circle bands per side. Thats around 3,000# breaking strength per side.Thje spec I couldn't get was the "pounds of resistance per inch" This value is really nore important than breaking strength I think. It's akin to arm wrestling. More important to resist than the breaking point of the fore arm bone.
Talking to my aluminum welder, he suggested we purposely engineer a weak point in the A-frame. He reasoned it better to fail there than rip holes out of the transom, at the mounting points.
Thanks,

[Laursen]

I have a few concerns one tow a 24 ft boat stern first is going to be a huge resistance
two. the amount of movement of two vessels at plane is quite incredible even thou it appears that it is not (inquire with the water taxi from Australia the slinky one ) if one were to theorize I would suppose if one constructed a fifth wheel kind of mechanism like they do on a animal trailer not the RV kind you may get a enough movement if I remember right there was a fish farm tug out on the west coast that had a concept like that. might of even been in Canada never mind the stresses of a large vessel passing anything that is ridged will not hold and if it does it will not be for long
I have seen alot of ideas come and go as both a builder and as Tug Skipper for many years The forces in a lock system is unbelievable and are not evident until you are running double or triples tied to each other

I have seen in the panama system during a storm that the front stanchion was ripped right off the barge and it had four inches of steel hanging from it and the rest of the mount area was intact on the barge :eek:

Frank Laursen

[ted655]

:) Thanks. I'm not towing anything stern first. It was a proposel by another, thinking out loud.
At best, a towbar/ball is the most weight & complication I want fastened to the stern of the HB. It wasn't stated but, neither boat will plane. 3-5 knots is tops.
All any of us can do on this planet is to design & engineer for the "reasonable".
Anytime we try to best Mother Nature, we lose, BUT nothing would be built if absolute success was the criteria. We've been thru 2 major hurricanes. I know what can happen, I choose to focus on what is reasonable prudence. If caught in a storm as you have experienced, the first thing I:) 'd do would be to unhook from my tow and spend my efforts on just surviving.
Anything can be underbuilt OR overbuilt. I'm looking for that spot inbetween.