Boat Lift Modification to support stub keel sailboat

[Seahorse24]

I have been researching boat lifts and trying to determine a way to modify an existing power boat lift to accept a Yankee Seahorse 24. From what I have been able to determine and from studying the trailer the boat is currently on, it appears most of the weight of the boat is supported by the stub keel, which is approximately six feet in total length and 12 inches wide at the widest part. My understanding is the bunks on the sides are mainly there to keep the boat from tipping over, according to what I read on the Internet.

My son and I have an existing boat lift that has bunks that are the same length as the existing bunks on the sailboat trailer. It appears all we need to do is to add a support for the stub keel and raise the bunks to the correct height and locate them under the hull at the correct points.

My plan is to laminate twelve 2X4s on edge for the stub keel support. The boards will be glued and screwed together and held in place by angle iron on the sides and both ends. I have measured the distance from the front of the stub keel to the front bunks on the existing trailer and that distance is 18 inches. We plan to use the trailer dimensions for locating bunks and the stub keel support platform on the lift.

I have attached a photo of my modification plan. If anyone has every tried anything like this, I would appreciate any thoughts or concerns. The cost of the modification is approximately $600.00 dollars for all of the materials. My son and I plan to do the work ourselves. Before we start spending the money, I thought it would be a good idea to get any feedback from experienced sailors, who may have used lifts before.

We plan to paint the boat bottom within the next few weeks and modify the trailer as well. We will apply two barrier coats of CM-15. One coat black, one coat light gray, along with a final top coat with a suitable paint to protect the barrier coats from UV.

I appreciate any comments. We have two other lifts that support power boats, but this is our first sailboat and we are learning as we go.

 

[McIntoshUSA]

Our lift is similar but actually made for a sailboat. I don't think you can see it but under the board (under the keel) is a medal beam. You can also see the stanchions on the sides that stabilize the boat. As you said most of the weight is on the keel. I have seen people convert existing power boat lifts (like yours) over to sailboats. (no cut down for the keel) In this case they usually put a support beam like you are suggesting (usually medal with a board on top) then they would have longer stanchions than ours to stabilize the boat. I am not an engineer, you just need to be sure that the the boards turned on end would support the boat. I would think that you would want something bigger than 2"x4", Maybe at least 2"x6"s - 2x10"s
Good luck.

 

[watercolors II]

Looking at your drawings added to the photo of the existing boat lift, I would say that 2x4s on end would be over kill if the keel bottom is the size and shape as your drawing and in almost the same location drawn. The two angle iron cross members attached to the outside frame and carrying the whole load of the present lift sitting on the inflatable tubes should carry the load so, that just two 2x10 bolted flat on these cross members would be enough, if these two cross members are of the same weight as the outside frame.

You are correct in thinking the weight of the boat sits on the bottom of the keel. With the keel sitting across the lifts crossmembers then they become the weakest point in this whole sit up. Additional crossmembers would transfer the load to the tubes and the outside framework.

 

[Seahorse24]

Thank you for your response and photo, McIntoshUSA. I used a calculation chart to determine the weight bearing of the 2X4s turned on their sides and laminated. I got the idea from a sailboat trailer I saw online. According the chart I used, the boards should be adequate for the boat weight, but I will double check that again, just to be sure.

Great photo of your lift. Our lift does not have the recess, and the boat will sit high above the waterline. I hope that does not present a problem. The only way for us to get into the boat while on the lift would be to use a ladder. We will probably lower the boat before getting on board.

 

[Seahorse24]

Thank you for your response, Watercolors. If that would work, two 2X10s would be cheaper and easier to implement. I will certainly look into that solution.

The current trailer setup uses 2X12s cut 18 inches in length stacked end to end. Each end rest on angle iron. So I know that a 2X12 on an eighteen inch span will support the weight. The lift has 46 inch spans between those cross members. So I was a little bit worried about laying the boards flat across 46 inches instead of 18.

I could try four 2x8s. Two stacked and both stacks side by side to give me 15 inches in width.

That would be less expensive and easier than laminating 12 2X4s. I'll look into the load bearing capability of that setup. I might have to add additional cross members to shorten the 46 inch span.

 

[Joe]

I would modify the entry end cross beam to something similar to MacIntosh's mechanical lift, This would allow you to lower the keel block to sit between the cylinders, rather than above them, It should add stability and reduce the pressure on the bunkboards.

You would have to build a channel to guide the keel into position.

 

[Seahorse24]

I would modify the entry end cross beam to something similar to MacIntosh's mechanical lift, This would allow you to lower the keel block to sit between the cylinders, rather than above them, It should add stability and reduce the pressure on the bunkboards.

You would have to build a channel to guide the keel into position.

Thank you for your response and suggestion, Joe. That channel would certainly be more ideal, but that modification would be difficult to do with the lift already in the water. At least three cross members would have to be cut and new V-channel steel welded in place. Also, we may need that space between the tanks to add additional flotation to the lift. I think we may
be cutting it close with a 4000 pound lift capacity.

We can add 900 pounds of addition flotation, but I don't want to spend the time and money, unless we have to. The added flotation is encapsulated and basically compensates for the weight of the steel structure. In other words the lift itself has to weight more than 900 pounds in order to sink, if we add the additional flotation. Unfortunately, we sold an air cylinder that would have worked perfectly between the two existing cylinders. We didn't think we would ever need that spare tank.

My modification plan can be implemented with U-Clamps. Any welding and cutting necessary on the angle iron added to the lift can be done on shore before we take the parts down to the dock. I think if the lift modification works, the boat will be stable once lifted. The boat is stable on the trailer, so it should be stable on the lift. Those white posts on the sides of the lift will be adjusted to align the boat as it enters the slip. The two posts on the front of the lift will be set to stop the boat from going past the optimum position for the lift.

Of course, we won't know until we try it. If this lift doesn't work, we'll look for a used lift better suited, but none are currently on the market in our area. The last new lift we purchased cost twice what we paid for the sailboat, so we are trying to use a lift we have.

 

[McIntoshUSA]

Great photo of your lift. Our lift does not have the recess, and the boat will sit high above the waterline. I hope that does not present a problem.


I have a neighbor with a setup like you are proposing. It is not a problem. It just means that your stanchions to support the sides of the hull need to be longer.

 

[watercolors II]

I would go as simple as possible and add supports when all of the other problems of the systems lifting the boat, the alignment of the keel, and the wave action on the boat sitting so high as compared to a lighter boat sitting so low as before.

The keel spanning the 48 inches is no problem if the two present crossmembers are strong enough to carry all the hull weight.

 

[Crazy Dave Condon]

I have been involved with designing lifts for sailboats over the years. I would suggest two more beams under the keel tray.

 

[Seahorse24]

I have been involved with designing lifts for sailboats over the years. I would suggest two more beams under the keel tray.

Thank you for your suggestion, Crazy Dave Condon. I've been wondering about the load on the existing beams. The center of the stub keel is going to be sitting on top of the side to side beam #2. I'm calling beam #2 the second one back from the front end of the lift. The side to side beams are about 48 inches apart. Do you think I should add the two additional beams so the gap between beams is no more than 24 inches.

They would be fairly easy to add. I might go with square steel instead of angle iron. I plan to use U Bolts on the sides to secure them. I was told it is a health hazard to weld galvanized steel.

 

[Seahorse24]

Great photo of your lift. Our lift does not have the recess, and the boat will sit high above the waterline. I hope that does not present a problem.


I have a neighbor with a setup like you are proposing. It is not a problem. It just means that your stanchions to support the sides of the hull need to be longer.

Thank you. That is good to know that your neighbor has not had problems with a similar setup. The existing stanchions are pretty tall. According to my measuements, they should work, but if not, we can add longer ones. They are made from 2 inch square steel tubing.

The floor of the dock is about twenty-two inches above the waterline. I'm estimating, depending on how thick the stub keel platform ends up being, that a four foot step ladder will be required to climb into the boat when it is on the lift. Sitting on the trailer it requires every bit of a five foot step ladder to get into boat.

 

[Crazy Dave Condon]

I would also ask the manufacturer of the lift first placing crossbeams on their main frame, will it be sufficient for the load. Do that first for the safety of your boat but most important for you. I do not want to read an obituary.

 

[Seahorse24]

Stub keel support platform

Here is a photo of the stub keel support platform we will attaching to the center of the lift. I went with four 4x4 treated posts instead of 2x4s. Glued and bolted together. It has to support 3000 pounds. This platform will sit on 2.5 inch angle steel spaced 53 inches apart.

 

[Crazy Dave Condon]

Seahorse, do your homework to include the manufacturer suggestions because it only takes one incident and someone could get hurt or even killed. Consider the safety of your son and you sir.

 

[Seahorse24]

Seahorse, do your homework to include the manufacturer suggestions because it only takes one incident and someone could get hurt or even killed. Consider the safety of your son and you sir.

Thank you for your concern, Crazy Dave Condon. I completely understand your recommendation. We have researched the lift extensively.

Total displacement of tanks completely submerged = 5600 lbs

Subtracting weight of steel and tanks, with margin allowed for tanks not being totally submerged allows the lift to be rated for 4000 lbs.

We are adding 200 pounds of wood and steel, thereby reducing the lift capacity by 200 pounds.

The boat displaces 2900 pounds. Add 250 pounds of gear and a 60 pound outboard. That means we need to lift 3210 pounds.

3800 - 3210 = a margin of 590 pounds.

We can add 900 pounds of lift capacity, if necessary.

We own three boat lifts. This sailboat weights less than our chaparral with a huge Chevy V8 engine.

The lift will either lift the boat or it won't. The manufacturer told us the lift is rated for a maximum capacity of 4000 pounds. We are under 4000 pounds. As long as we do not exceed 4000 pounds, the steel frame and tank supports can handle the load.

We will have a stub keel platform that displaces the load across the two center steel angle pieces that are attached to the tanks. We are adding two more cross members. In addition we will have twelve foot bunks reinforced with steel on each side that are attached to the four corners of the lift. These will take a portion of the load. We also have the option to increase the lift capacity by adding a third tank along with more steel.

I don't know what else to check on if the manufacturer tells us the lift is rated for 4000 pounds as built. The lift is out of warranty and they do not take responsibility for any modifications we make other than to state the lift's original design capacity.

I think it is worth trying to use one of our existing lifts before we spend thousands of dollars for a larger lift.

We will be standing clear when we attempt the first lift. I would not risk lift and limb for a boat.

 

[Crazy Dave Condon]

It is refreshing that yu are thinking thru on this and safety is most important as many do not take that into account. I wish you well but keep us posted.

 

[Seahorse24]

It worked. Our sailboat is now in the slip sitting on a lift.

 

[Seahorse24]

Here is another photo.

 

[Crazy Dave Condon]

Great job