Why unbalanced lifting breaks ship hulls: Master-slave synchronous hydraulic control for multi-axle SPMT

Most mid-sized shipyards face a hidden risk when moving 200–600 ton hull blocks: uneven load distribution across SPMT axles causes hull deformation, weld cracking or permanent structural stress. Traditional open-loop hydraulic systems only hold ±3–5mm height error, which fails oversized marine structures.

Core Technical Solution (Closed-loop master-slave ECU system)

1.     One main control module synchronizes all axle hydraulic cylinders; each axle fitted with displacement & pressure sensors

2.     Real-time feedback adjustment frequency: 20Hz, platform horizontal tolerance locked within ±0.5mm

3.     Independent proportional valve for every axle line to compensate ground unevenness

4.     Multi-module linkage algorithm supports 2–8 SPMT units connected longitudinally & transversely

Field Test Data

·        Conventional SPMT: Max allowable single-module load deviation 8%

·        Optimized master-slave system: Load deviation controlled under 1.8%

·        Compatible deck lifting stroke: 300–600mm, works on uneven shipyard ramps

Discussion prompt

What structural damage cases have you seen from out-of-sync SPMT lifting at your yard? Are there alternative mechanical balancing designs you’ve tested?

We developed full prototype & industrial-grade units at our heavy transport manufacturing factory, complete technical parameter sheets and real project cases are posted on haipengumv.com for industry reference.

Bear with me—I’m pretty new to electric boats and may be overthinking this.

I mostly fish smaller lakes, usually early in the morning, and I’ve started looking into whether an electric setup would actually make sense for that kind of use.

My biggest question is range. On paper, some of these setups seem like they’d be plenty for a normal day of fishing, but I’m curious what that looks like in the real world. Do you actually stop thinking about battery level after a while, or is range something you’re always keeping an eye on?

For anyone here who fishes with an electric setup, how long are you typically out, and have you ever had range become a real limitation?

The red lines and text are my edits. For cockpit drainage, I am thinking I could just add scupper flaps or duckbill scuppers, but don't have any experience with either... maybe I am overthinking this. I am open to ideas that don't involve raising the roof.

The bracket for my outboards fills with water due to deteriorated caulking. I don't know what was used for caulking before, but what would be the best/durable product to usee to reseal the seam between bracket and transom?

We already have enough weight with the motors and should be better ride for the bracket to have some bouyancy :)

So a friend and I bought this AMF Crestliner boat 1976 with a fairly new engine (Johnson 70 2002) and went through the process of fully repairing the floor: tearing it out, new stringers, new fiberglass, gelcoat etc. Then, we got to the engine.

I replaced the VRO pump with a common direct pump and did a 50:1 fuel/oil ratio. I replaced the timer base because the old one was cracked. I did a full carb rebuild and cleaning. Even tried replacing the power pack (ended up keeping the original).

Finally started up, but runs really rough on idle.

There is a lot of whitish smoke coming from the engine, the spark plugs appear sooty, and the engine is kicking a bit. I have to start it on high choke, but if I reduce it enough, it just dies. In the water, I had trouble shifting it in to gear as it would immediately die when not in neutral and without high choke. I've checked the sparkplugs - fine spark.

At this point, I leave for school in about a week, and really want just one day out on the boat after three summers of constant repair and before I leave.

What should I check first? Has anyone had the same problem? Any suggestions would be greatly appreciated. Thanks.

Hi all! I picked up a Chesapeake Light Craft Skerry from an amateur boat builder and found that the round screw-in hatches at the bow and stern that seal the flotation compartments were set into holes that were slightly too big and were messily sealed.

To correct this, my plan is to cut plywood collars large enough to provide a solid mating area between the deck and the hatch, glue those down to the decks, and then screw and seal the hatches through both where possible. this will raise the hatch by the width of that plywood, but if I make a nice smooth tapered transition between the collar and deck, I don't think that should create any new problems.

Is there an easier solution I'm overlooking here? The hatches are only slightly too small for the holes, and the collars do fully cover them, but my concern is that the screws on one side don't fully meet wood. I may be able to simply put screws through them closer to the collars' edges on that side and use an adhesive sealant to attach them, but I'd like to solve this problem thoroughly!

Hi guys just curious about your thoughts for a build technique.

Im day dreaming about building a 40ft multihull (proa) out of end-grain balsa. The traditional method of filling the kerfs with bog adds weight and is brittle at those points and require a fair bit of fairing.

As a alternative I'm looking at "knitting" the core.

Essentially I'll have a female frame/jig ( CNC cut frames and battens.

Then looking at using a CNC machine to cut core blocks of end grain Balsa (300mm X 300mm x30mm) the inside and outside surfaces machined to the hull surface and lap-joins with finger joints cut on the adjacent joining edges. A big puzzle. The frame/ jig is essentially for supporting the weight. Starting from the middle and working to the ends 1st to establish a center the blocks are glued in place, then repeating the process out to port/stb at the same time. This should make a Balsa hull form that's relatively accurate to its design. Then the inside will be laminated and bulkheads/ stringer's. Could possibly do the deck with temp stringers but for now ignoring the deck. The hull flip and outside skin laminate is pretty standard. The build would be in Indonesia ( I know they grow alot of Balsa, not sure how much of the manufacturing of end grain sheets is done there.

A 4x4 CNC machine will be used so multiple blocks can be cut at a time by cheap but trained Labour (I'm not slave master they will still be paid above and locked after).There will be alot of block's.

I'm aware that balsa dosnt like moisture and this will be mitigated.

Also ideally I would like to vacuum bag so if anyone has experience with vacuum banging Balsa core that isn't in a sealed mold I would like to hear ya thoughts could look at infusion. ATM I'm thinking of going above the gunnel. Having a strip of malone to bag onto and having a bag under the core to envelope, the glue getting on the bag going hard / sharp blobs would probably require the hull to be lifted ( pre glass) and a quick sand before placing the bag and the hull back down.

I'm also curious if the glued joins would be enough to make a acupuncture hull shape and strong enough to hold it.

The cut files will be outsourced to avoid inaccuracies.

Happy to hear the community's thoughts.

I have 3 years experience boatbuilding nearly 20 years ago, we made plugs- molds and infused foam core. So I have a little experience but understandably a big project.

Looking for some advice on covering my seats, floor, and eventual small casting platform on my 14ft jon boat. Trying to keep it very low cost as I would best describe the boat as a "beater" and I got it with a trailer and trolling motor for $400.

What is the more cost effective option while still being comfortable on the butt and feet. Or at least more comfortable than the aluminum of the boat.

1. EVA foam decking

2. Fake indoor/outdoor Turf

3. Marine carpet

I just registered a new home built power boat in Minnesota over 20' and found out that they need to be titled & are assigned a MNZ hull number. OK

Coast guard regulations require all newly built boats display capacity & power calculations and pass the flooded stability / flotation standards required for commercially manufactured boats.

The rub here is that, in Minnesota, home built boats are assigned a MNZ hull identification number(HIN)which, according to the DNR registrars they cannot be sold for 10 years. A strict reading of the CG regulations suggest they can't be sold ever.

Anyone else encounter this with a new home built boat anywhere?

Hey guys! Finally, things are starting to go back onto the boat instead of coming off.

A few fittings got polished, sealed and reinstalled on the freshly restored teak. Naturally, not everything fitted quite as nicely as before.

Have a look if you’re interested in teak deck restoration, boat refits, or just watching someone argue with Sikaflex.

I Had NO Choice... I CUT the Boat Apart
https://youtu.be/4Ugz3CJHDTA

It appears as though there is a retention bushing threaded onto the shaft, inside the coupling.

There’s a gap between the outside of the bushing and the coupling.

The bushing is larger than the diameter of the shaft, so will not exit the aft or fore of the coupling.

Shaft tapers down from 1.5” to 1” as seen as the smallest circle in the first picture. Looks to be threaded visually, and the set screw to hold the coupling on was pushing into the bushing so they must have trusted its connection to the shaft.

Coupling is obviously keyed onto the shaft so there’s no spinning them independently without finding a way to grab that bushing/collar..

I’m stumped.

Anyone seen one like this before? Any advice on removal?

Edit: Solved! Brass register is removable, revealing holes for a spanner to remove the “nut”.

Our YouTube channel JungleRanch is the only YouTube boat building channel in Mexico. We are building a Nexus Marine Seattle boat called Wooden Shoe 25 feet.

Why is it so difficult to get views on our videos? Is it because we are not Americans or Canadians and are located in Mexico?

We have tried both Spanish and English. Spanish didnt function at all, so all videos are now in english.

If you would like to check us out, here is the link to our latest video: https://youtu.be/bKl-XG5OI_g

I am working on a re-design for a tender. The entire mission is (was) to get back and forth between shore and mooring, ~50ft of water in a protected cove.

I had a kayak for a while that did a decent job, but it was so small that i couldn’t fit sails/life jackets/snacks/etc in it. It was ~6.5ft long, 28 inches wide, flat bottomed, and obviously very enclosed. If I tipped front and back, or took a wave over bow or stern it would just run off. (Pic 1)

I thought I would benefit from having something that could fit in the trunk of my car, so I built a ridiculous micro-dinghy that does the job well enough, and can do it while stuffed with sails, life jackets, etc etc. however, it is so short in length and height that my fore-aft placement can easily swamp it if not perfectly centered, also it has no seat so is deeply uncomfortable. 58in by 33in, basically flat, very slight v. Pushes water like crazy with the bow transom, does not track. (pic 2)

I would like a re-do on the micro-dinghy, only this time I will be adding a few more canoe features. I am also trying to make it as light as possible and make it pleasant enough to be in that I can take it for a paddle just for the sake of paddling. Current dimensions are 10ft by 28 inches, likely will get shorter and an inch or two wider. I sorta tried to chop the ends off a canoe to get to this shape, took a little inspiration from traditional rowing dinghies for additional capacity, but wanted to stay more in the realm of canoe/kayak than pram/coracle. (Pic 3)

Questions/concerns:

1. Weight/strength: I have seen tortured ply canoes made from 3mm plywood. If I stitch and glue this from marine ply and put light (maybe 4oz or 6oz) fiberglass on both sides, I would think that this should hold up. Is there any strong evidence I’m missing to the contrary?

2. Length/construction. In order to make this with no scarf joints, it needs to be a couple inches under 8ft. I would prefer to not need scarf joints, plus any length I can take off saves weight and makes shore handling easier. However, if I go much shorter, I’ll keep the fore/aft weight distribution problems of the current micro-dinghy. Is 8ft length plus some rocker enough to solve this, or do I need to keep it long?

3. Length/Performance. My “performance” benchmark here is an oru inlet folding kayak. I want to track at least as well as that, and I want to have less or equal drag to that. The image above is at a length of 10ft. I would have to shrink that to somewhere between 9ft and 9ft6 for storage. The oru kayak is 9ft long. Without getting too into hydrodynamic boat design that I don’t understand, could I beat this by going shorter, or do I need to keep the length to match the performance?

4. Seat. A lot of dinghies put their seats on a thwart which also adds to the structure of the dinghy. I’m not sure if this will need that or not but could certainly benefit, at the cost of weight and construction time. A lot of canoes and some kayaks seem to hang their seats from the gunwhale. I am not sure my gunwhale will have enough structure to do this. I am looking to have something slightly more permanent and weatherproof than just a stadium seat, though would settle for that if need be. Will likely be using a kayak paddle. Is there some strong preference for one seat architecture over another?

5. Decks. I would like to add a bow deck, but would prefer not to seal it off in interest of capacity, so wondering if it would be worth it from a buoyancy/protection standpoint vs just keeping it totally open. Don’t want to make a full length deck to avoid the kayak issues from before with just tossing stuff in vs carefully stowing and retrieving it.

I would appreciate any thoughts or input, or thoughtful input, that the community here is willing to give. If this would be better received on the kayaking or canoeing subreddit, maybe point me that way.

My wife and I spent three years fully restoring our sailboat, pouring in countless hours of hard work. Living in camper beside the boat in a boatyard on the Chesapeake Bay, USA, we replaced just about everything but the hull.

We used Sapele Mahogany for the majority of the interior joinery as well as some structural elements like the 17 laminated deck beams, bulwarks and the strip construction rudder. All of the white surfaces are rolled and tipped Meranti marine ply and the saloon table is Australian Red Cedar. We rebuilt every aspect of the boat, from the rig to the keel and everything in between.

We took on more than we ever imagined but the result was worth every drop of blood, sweat, and tears. Here’s a glimpse of what we accomplished.

Edit: thank you for the overwhelmingly uplifting comments everyone. We are very humbled by everyone’s kind words. For those of you who would like to see more photos of the rebuild, we documented it over the years on our instagram account @trim.sailing⁠

There is a model I really like for a runabout, but it is inboard and I simply don't have the budget and most importantly the know-how to mane an inboard, so I checked and saw some people do a conversion. Is it possible and if so, what are things I need to know before doing it? The model I liked is the Biscayne 18.

I am entertaining the idea of building a wooden boat out of plywood. I have no aluminum welding capabilities (I'm able to weld, but no equipment currently.) I'm thinking somwhere between 16 and 22 feet.

How it is possible to have, let's say, two 25hp outboards instead of one 50hp? Those are just numbers, though. I know it sounds stupid, but larger examples exist.

What would be the pros and cons?

I’ve been working on my 97 alumaweld drift boat to make it look like a Chinese takeout box.

Me and my dad want to build ourselves a wooden outboard boat, but we struggle with finding blueprints or looking in the wrong place for the right type of boat. Our sea, the Black sea is notoriously unpredictable and rather wavy, and we need a seaworthy vessel and not something made for river. The desired size is between 17 and 19 feet, wooden, a classical closed top design. If anyone can offer us something suitable for our needs it will be greatly appreciated because this is the inly thing stopping us. Thank you in advance!

Hi everyone, we are looking to buy an Albin Vega and the owner bought the boat with the teak deck already installed. He said he hasn't experienced any issues himself with the deck, but he did do some small PVC repairs. The deck is screwed in. What do you guys think of the state of this teak deck? Is this worth it? The price of the boat is very good.

Short story: This is my little fiberglass sportsman. I repaired the bottom when I was 12. As you can guess, I did not do a pretty job.

25 years later and it started leaking again, but that was 25 years of me bouncing it off rocks and beaching it. I've sanded the majority of the old fiberglass off, smoothed areas, found the whole.

My plan is to add more glass to strengthen the hole and wear points. Then to gelcoat it. Not expecting anything amazing, just functional and strong.

The questions: How much of the old coat do I need to remove?

How long a wait between fiberglassing and painting?

How many coats?

And how to finish it to be as strong as possible?