Davit system for Tomcat

Beflyguy · Posted: Sat May 01, 2010 7:17 pm Post subject: Davit system for Tomcat

Been thinking about a davit system for the top of a Tomcat. I want to be able to easily put a hard shell like a Water Tender 9.4 upside down on the top. I may start with a Yakima rack or build from scratch with 1" stainless. The davit will essentially hold a rope or small cable out from the top and side, the dinghy will be lifted out of the water and up until it contacts the davit arm, then the Dinghy will flip onto the top of the cat. I think if I install the lifting points correctly in the dinghy, it will be possible to tilt it and wash the inside of sand etc, before flipping it onto the roof.

Specs on the Water Tender 9.4 are:

112"X55"X15.5" 115lbs Capacity 480lbs Max 5hp $549 at WM

toyman · Posted: Sat May 01, 2010 8:39 pm Post subject:

I thought of a similar setup for the 25, but don't have access to any fabricators I trust, nor do I have my own facilities. I assume that the boom standing Horizontal in the first sketch will follow the dinghy up until it contacts the vertical mast. The dinghy will be "on it's gunwales" then it will lay upside down on the cabin top...

Beflyguy · Posted: Sat May 01, 2010 9:27 pm Post subject:

thataway · Posted: Sat May 01, 2010 10:11 pm Post subject:

Could it be done--yes. Is it going to be practicle? Not so sure of that. Generally this type of lift with a hard dinghy uses two lifting points. What you show seems to use a gin pole type of device to transfer the load on the horizontal arm as you lift the dinghy. Lifting 115 lb dinghies is a bit more difficult than you may think. A winch system will probably work best. Block and tackle are do-able, but get complex. You also have to stabalize the gin pole, and then pull it down to flat over the cabin top (actually it will have to be a bit above the cabin top crown) You have to hoist the boat to the horizontal arm, then tip that arm up, slide the whole rig over and tip the boat back up side down. The process is reversed to launch the boat. As you have found out; the side decks are narrow and not easy to balance on. The other question is are the hand rails you are using as a basis, adequately supported for the weight of the dinghy. The side parts of the tops (at least on my boat) is not cored--the center part is. It is possible that you may end up increasing the bearing surface of the SS railing on the cabin top.

I would work out all of the details with models first. I have carried hard dinghies and RIB's on larger boats. They are not easy to hoist aboard, unless you have a crane davit, or mupltiple davit system.--even with just over 100 lbs.

On another but related subject: You were going to go with a 1 1/2" greater pitch prop--based on a very lightly loaded boat. It appears as if you are going to be substantially increasing the loaded weight of the boat.

Dreamer · Posted: Sun May 02, 2010 1:20 am Post subject:

Beflyguy,

Les at EQ Marine makes a nice davit. Doryman and SeaPal have them installed. No need to reinvent the wheel/davit.

rogerbum · Posted: Sun May 02, 2010 9:07 am Post subject:

Roger - that davit won't tip the boat over which is what he's trying to accomplish. However, that davit plus a more typical inflatable might be a better solution. My guess is that he wants the hard shell dinghy for it's longevity and the hard shell is what is driving him to want to turn it over. An alternative is to have a cover for the dinghy and leave it upright. That would require some racks on the roof to keep the dinghy from rocking but would be the simpler solution.

Dory-Ling · Posted: Sun May 02, 2010 1:24 pm Post subject: Davit system for Tom Cat

Not having an album nor knowing how to put pictures in post, ve put 2 in the Library of a diavit on our 25 ft. (cockpit & accessories then detail pictures, then back page.) Theres no reason this would not work on tom cat too. Ve like the cleaness of it and use it to load dingy(sometimes, not that old yet) and to pull shrimps pot.
Martin

Captains Cat · Posted: Sun May 02, 2010 3:25 pm Post subject:

For those that had trouble finding Martin's pictures, here they are:

Very nice Martin! I am sure that folks will want to know brand, etc, etc.!

Charlie

Doryman · Posted: Sun May 02, 2010 5:00 pm Post subject:

Captains Cat · Posted: Sun May 02, 2010 5:03 pm Post subject:

They looked fine when I previewed them. Will try again.

Warren, can't help you. Someone took them out of the album. When I went back to get the properties again, they were gone.

Sorry

Charlie

toyman · Posted: Sun May 02, 2010 6:29 pm Post subject:

I saw them and it was a NICE setup. Load carried thru the roof of the cabin port side aft - looked to be ~4" column.

Dory-Ling · Posted: Sun May 02, 2010 7:47 pm Post subject: Davit for tom cat

Sorry for the confusion people. When I saw Charlie put them on the post I deleted them from the other location to elimenate redundancy. I will replace them.

And they are back now, sorry again. Rolling Eyes

As penance for my problem, I put one showing the hauler too. (in the library)
Martin

thataway · Posted: Sun May 02, 2010 8:47 pm Post subject:

Martin's set up is what is done in most crane davits on trawlers and sport fishers etc. It is a good engineering solution to the problem. The cabin aft bulkhead takes the lateral load and the cabin side takes the fore and aft loads. Downward load is transimtted to the floor. It is a clean and elegant solution to a problem--now with a winch on the davit arm, it would lift a dinghy easily.

But there is also the effect of an extra 100 to 130 lbs on the top of the boat. Does it make a difference? Yes, especially in beam seas at slower speeds.

Dory-Ling · Posted: Sun May 02, 2010 9:05 pm Post subject: Davit system for Tom Cat

Total weight of this davit including the cylinder full of oil that the thrust bearing runs in is under 60 lbs! And with a small (3/4) block set up DOES lift the dingy easily.
Martin

thataway · Posted: Sun May 02, 2010 10:09 pm Post subject:

Martin, it was not just the 60 lbs of the davit system, but the 100 to 120 lbs of dinghy and racks etc. (some up to 150 lbs) which is being added to the top of the C Dory which may be of concern. Is it unsafe--most likely not. But as you add more and more weight, it will affect handling.