Ski Tow Mount Point Help Needed for Old OB

[mtboatin]

I purchased a old '56 AlumaCraft Deep C which is 15' and has a 50hp Evenrude and a the aqueduct transom on it. My 9 and 11 year old girls are wanting to tube and maybe attempt to ski some day. The few times I've had it out I think she should do ok if kept within reason. My problem is there are no existing rings on the transom to attach the bridle to. I want to know if there are any dos or don'ts in installing these hook points. How high or low should they be positioned and how wide or narrow, or does it even matter?

 

[metriccrescentwrench]

Re: Ski Tow Mount Point Help Needed for Old OB

What's an aqueduct transom, I've never heard that term?

Use big, thick washers on the inside of the transom to spread the load. Or even better, fabricate a small steel plate that matches the holes. I believe I'd mount them as high as possible on the transom. And most important - do a good job of sealing everything with 3M 5200, you absolutely don't want any moisture getting into the transom.

 

[Chris1956]

Re: Ski Tow Mount Point Help Needed for Old OB

Also, look for a reinforced area of the transom to attach the eye hooks to. A lot of the aluminum boats have thin skin in lots of places. Consider a large piece of plywood to spread the load, if the hull is just thin aluminum.

 

[mtboatin]

Re: Ski Tow Mount Point Help Needed for Old OB

Thanks for the quick responses.

I believe AlumaCraft was the first to have and patent the aqueduct transom. It was a catch shelf for water coming over the transom that has drain holes to expel the wash over back out of the boat. Part of the reason I noted this is to let readers know it's a little beefier than the typical aluminum boat of this age due to this clever little system.

So high a high mount on the transom is desired. Is width a concern other than clearing the OB? I would think the narrower the better so when pulling from a single point the boat direction would not be effected as much. I may just have to take a bridle and see how wide or narrow it would allow for, especially when pulling a device at an angle.

 

[metriccrescentwrench]

Re: Ski Tow Mount Point Help Needed for Old OB

I would think the narrower the better so when pulling from a single point the boat direction would not be effected as much.

How far apart you put the eyes will honestly not have any measurable effect on that. Just figure out what works as far as clearing the engine.

 

[haulnazz15]

Re: Ski Tow Mount Point Help Needed for Old OB

I would put the tow eyes as high and far apart on the transom as possible. The wider they are, the better the pulley on the bridle works as the ski/tube moves from side to side out of the wake.

 

[Chris1956]

Re: Ski Tow Mount Point Help Needed for Old OB

Thru bolt the eyes with large washers or plates, on the part of the transom sandwiched by wood.

 

[emoney]

Re: Ski Tow Mount Point Help Needed for Old OB

How about considering a "ski pole" set-up? Most of the ones I see will give you a 3 point mounting system and then you have the height issue handled as well. Pulling a tube/skier/etc. is a lot of load on a transom and more you can get that load dispersed somewhere else, the better off you are. That's why many modern boats have a ski pole.

 

[haulnazz15]

Re: Ski Tow Mount Point Help Needed for Old OB

How about considering a "ski pole" set-up? Most of the ones I see will give you a 3 point mounting system and then you have the height issue handled as well. Pulling a tube/skier/etc. is a lot of load on a transom and more you can get that load dispersed somewhere else, the better off you are. That's why many modern boats have a ski pole.

Modern boats have a ski pole because they are trying to emulate inboard ski boats. You cannot tube off of a ski pole, it is dangerous and every ski pole I have seen has a warning sticker advising against it. Transom eyes in the transom are stronger than the ski pole on any boat is. The transom eyes are commonly used to lift the entire boat out of the water in some applications.

 

[mtboatin]

Re: Ski Tow Mount Point Help Needed for Old OB

Thanks for all the input. My plan is to use transom eyes at this time.

Next question. Should I use 3/8" or 1/2". I'm a bigger is better type of guy but I don't know if on a boat this small it makes much sense to go with the 1/2". I'm looking for ones that have the larger SS plate on the back side for sure. I've seen some with smaller plates which I don't want.

 

[Bob's Garage]

Re: Ski Tow Mount Point Help Needed for Old OB

Thanks for the quick responses.

I believe AlumaCraft was the first to have and patent the aqueduct transom. It was a catch shelf for water coming over the transom that has drain holes to expel the wash over back out of the boat. Part of the reason I noted this is to let readers know it's a little beefier than the typical aluminum boat of this age due to this clever little system.

So high a high mount on the transom is desired. Is width a concern other than clearing the OB? I would think the narrower the better so when pulling from a single point the boat direction would not be effected as much. I may just have to take a bridle and see how wide or narrow it would allow for, especially when pulling a device at an angle.

View attachment 165277View attachment 165278

Alright, everyone else seems to be in support of your attempt. However, I am not.

If the tow eyes are to low it will tend to pull the tow rope down, making skiing attempts for a novice very difficult. Additionally, it will also make tubing difficult as it will try to pull the front edge of the tube down.

But that can be overcome. My concern is that the transom is not up to the task. I am concerned that the hull, due to it's construction will not support the stresses of the tow. The aluminum appears thin and the lack of a flat surface for reinforcement leads me to believe the hull will distort, damaging the boat, and possibly leading to a catastrophic failure.

I hope I am wrong.

 

[NYBo]

Re: Ski Tow Mount Point Help Needed for Old OB

For tubing, you want the mounts on the transom; for skiing, you need a higher connection point like a pylon.

I agree with the other Bob: Bolstering the transom is a must from the look of it. That's also a rather low transom so I would try to install the eyes as high on the outer corners as possible.

 

[mtboatin]

Re: Ski Tow Mount Point Help Needed for Old OB

Alright, everyone else seems to be in support of your attempt. However, I am not.

If the tow eyes are to low it will tend to pull the tow rope down, making skiing attempts for a novice very difficult. Additionally, it will also make tubing difficult as it will try to pull the front edge of the tube down.

But that can be overcome. My concern is that the transom is not up to the task. I am concerned that the hull, due to it's construction will not support the stresses of the tow. The aluminum appears thin and the lack of a flat surface for reinforcement leads me to believe the hull will distort, damaging the boat, and possibly leading to a catastrophic failure.

I hope I am wrong.

Bob, Thanks for the concern. This is why I'm on here to make sure not to do things I shouldn't be doing. The inside has about a 1/2"-3/4" piece of oak the outside is the 3/8"-1/2" plywood. I don't know much about aluminum thicknesses other than the research I've done seems to put the Alumacraft, back then, as one of, if not the best built aluminum boat of it's time in design and thickness. Yet the 15' hull only comes in at around 250 lbs. This is I'm sure much different than today's standards. The feeling I was getting from previous posts was to mount high and wide. The transom does have a shelf that connects to both sides of the boat and has two cast aluminum braces near the engine mount. Below the shelf is another cast aluminum brace in the center of the transom. The top corners of the boat have cast corners for additional strength. The pics may not be the greatest for showing this. It's rated for a 60 hp OB back in '56 and four person load. I have a '74 50 hp shown on it right now.

 

[Ned L]

Re: Ski Tow Mount Point Help Needed for Old OB

I'll just throw out something different to think about here. If you can get some sort of strap around the lower unit of the outboard that would allow you to clip the tow rope to that would be the best solution (other than it being a low point for attachement, which you aren't going to overcome with your transom anyway). This is not a silly idea, years ago there used to be commercially available brackets that were made to fit and go around different outboard lower units so you could clip your tow rope right to the back of the lower unit just above the water. They were two piece cast aluminum with an integral ring on the back. They worked great on small boats for skiing, there is ZERO additional stress put on the boat when towing this way, the skiier does not affect the handling of the boat nearly as much, and you don't have to drill any holes or add any permanent hardware. --Just a thought.

...
Thinking a bit more. On a small light outboard rig you would NOT want to be towing from a point above and in front of the outboard (i.e. towing pylon) because making a sharp turn could result in the boat being rolled over.

 

[haulnazz15]

Re: Ski Tow Mount Point Help Needed for Old OB

I'll just throw out something different to think about here. If you can get some sort of strap around the lower unit of the outboard that would allow you to clip the tow rope to that would be the best solution (other than it being a low point for attachement, which you aren't going to overcome with your transom anyway).

Attaching anything directly to the engine is a bad idea. You would be putting a ton of stress on the lower unit which isn't designed to have that stress pulling on it. I know about the old hoops they used to put around the old outboards, but they quit using them because it wasn't any more practical than using a ski bridle between the transom eyes.

 

[Ned L]

Re: Ski Tow Mount Point Help Needed for Old OB

Ah! I just found a picture of one that someone posted here a year & a half ago

These really do work well.

 

[Ned L]

Re: Ski Tow Mount Point Help Needed for Old OB

Stress on the lower unit?? All the stress is going through there anyway. In reality every bit of thrust required to move the boat forward starts at the prop and is transferred though the lower unit, through the motor mounts, through the outboard mounting bracket to the transom. This cuts off every bit of additional stress from towing at the lower unit and adds NO addtional stress to the motor mounts, transom bracket, or transom. This IS the least stressful way to tow with an outboard.
I suspect they stopped making them when the number of lower unit shapes really increased (1960's). We had one on a 1964 25hp Gale (on a 13'6" Old Town runabout) , it made towing a skiier much more pleasant for the operator.

 

[acarter92]

Re: Ski Tow Mount Point Help Needed for Old OB

I agree, that attaching it too the motor (something like the picture above) wouldln't be anythig but LESS stress on the transom, mounting brackets, etc... while pulling. However, if you were to "jerk" the rope, from not paying attention or for any reason (this shouldn't happen, but it does) I would think that would be a lot of extra stress on the mounting brackets, and maybe the steering too?

My vote would definately be to figure out how to safely mount some rings on the transom.

Just my 2 cents...
Austin

 

[oldjeep]

Re: Ski Tow Mount Point Help Needed for Old OB

I would think that a sudden tube nosedive would cause some issues with that setup. For a skier - fine, you dump you let go. For a tube digging in, that is a lot of force.

 

[Ned L]

Re: Ski Tow Mount Point Help Needed for Old OB

Hmm, interesting variable there. ..... So, if we think when towing from the transom, the tube (or whatever) takes a nose-dive, we are putting a real braking effect on the boat, with the outboard still pushing forward at full thrust. We have just put the transom, outboard bracket, and motor mounts under significantly increased compression force for a moment. Likewise, if we are towing from the lower unit and the tube (or whatever) takes a nose-dive, this puts a real braking effect on the outboard, and the 'boat' is still traveling forward at full speed, so there is then tension applied to the transom, outboard bracket, and motor mounts. Which is more 'stressfull'? - not sure, but definately something worth thinking about.