Custom 19' all weather, minimalist, strip plank composite 'go fast'

Could you make this into your barge and boat both SoCal?

 

Socal, IMHO a cat like the one in the video posted by Fallguy (or a slightly smaller version even) would be so much better in every way imaginable for the work that you are doing.
It would be (much) safer, more comfortable and dryer - and I am sure that it still gets pretty impressive fuel economy.
OK. your inflatable (or rigid version) will still have better mpg, but with the cat you would also then have an advantage of ridiculously good stability along with the option of twin engines - especially useful if you are going on longer passages offshore.
And if you were to ask your customers which boat they would prefer to go on, if they had a choice of your inflatable or a smaller version of the power cat, how many do you realistically think would choose the inflatable?
Some might enjoy sitting in a puddle in their wetsuit while travelling to their dive site, but others might prefer to have a bit more comfort.

 

The above catamaran barge does NOT satisfy the sor.

He frequently doesn't anchor to the bottom but to his waist. He toes the vessel while swimming.

 

One nice thing about the 3D software is I can get very easily get volume of all the portions of the boat, and I'm relying on that for many of my calculations. Since it's a rough model though I haven't modeled things like longitudinal stringer which would take up some of the volume under the floor so I have to account for that, etc. And yes, errors mean the boat most certainly does not do what I expected. Worst case I could add the 'sock' scuppers of my friend's old RIB. Here is a photo I found that shows them used on an inflatable. On his RIB they had clips so they were usually left up (closed) but if opened while underway venturi forces would drain any water on the deck almost instantly:

Actually, I'd love to get his info, thanks, just to see what his boats look like if nothing else.

Stuffing the bow is a concern of course but since are swells can large they are long period so around here it usually isn't too bad. I have stuffed the bow in the inflatable more than a time or two and it recovers, the other day in the bay I did it intentionally a few times all the way to a full swamping to see how it recovers... I am trying to design this vessel for that contingency; if the motor is operational and there is enough absolute floatation in the right places in the vessel it should recover and self bail quickly with no issues; when anything like this happens with the inflatable it is usually because either the weight distribution was very careless and we stopped in waves. That added weight makes the vessel sluggish but it has 2x - 3x the reserve bouyancy it needs to stay afloat, and as it fills with water the water is contained in the center of the boat so free surface effect is minimized and while I don't care for the way it handles it does actually get MORE stable the heavier it's loaded. The inflatable never actually broaches and that is part of why I like the long skinny thing--the inflatable does best in any sort of following sea, even very heavily loaded (provided the weight is kept as much aft as possible). A large wave breaking directly over the beam when it is heavily loaded is very alarming but those type waves are either happening very near shore (basically the surfline where I never have cause to go), or during conditions that for us are more in the category of 'storm', and even then it can be minimized by careful steering. One large consideration is that it is an inflatable--I have stiffened it with a heavy white oak timber running most of the length under the airfloor but it can still flex a tiny bit if the bow is pushed down. In short, much like running a kayak in the ocean, the weight on the boat has to be distributed with some consideration to sea conditions.

Yes, when the boat is swamping the crew will start to float. We experience this in the inflatable. The USCG minimum foam calculations actually take this into account for passengers and even engine; the weight calculations are fractions of the total weight. If passengers are scrambling to stay out of the water and stand on the console it would be more problematic but freedivers in wetsuits are not bothered. For all my calculations of bouyancy I'm ignoring the fact that the structural components are wood (and light wood at that), and that gasoline is lighter than water, etc, and just going off foam volume so as to have some extra margin.

I am going to build the wood model before I do any more CAD design but I did realize I need at least 4 cubic feet of foam total at the transom, some extending off the back of the transom like an inflatable and some foamy knees inside at the transom. This will in any situation or attitude offset the weight of the engine. Basically what I'm designing is a boat which when loaded very light (1 - 3 people) behaves somewhat conventionally and very sporty in most any sea or situation since there is enough floatation under the deck and relatively low center of gravity, ie surfboard. When loaded heavy, it becomes something that swamps to a certain degree at rest (overloaded surfboard) but then drains quickly when it starts to run and gets fast and efficient and dryish again, and will drain fast enough that even a fair bit of onboarded water while underway isn't too big a deal, but when loaded heavy it will swamp if stopped due to water coming in through the scuppers. Worst case, if disabled in a storm it would float level and be unsinkable since it has so much foam and the whole structure is inherently bouyant.

The airbox idea is good; at heart that's why the inflatable is fundamentally a good design from the standpoint of stability when swamped. I don't want to add a lot of weight and lose a lot of interior volume but the interior wall of the airbox could just be 1/4" WRC. With an extra 4 cubic feet of floatation at the transom, the airbox could be skinnier throughout most of the boat, and I'm already planning to make the boat 12% wider than originally intended so particularly in the bow compartments and at the fore that extra width will become foam. The bow needs to be very carefully thought out so that if it stuffs, water doesn't collect and make the bow too heavy; to be operable and seaworthy this design mandates that any water in the boat make its way quickly to the transom where it also drains very quickly. I don't want to go pram bow but you raise a good point, the nose even stuffed with foam isn't a lot of volume. When I started the design I actually measured a type 1 lifejacket and designed one of the front hatches to only just fit 5 lifejackets and no more, this will take up a fair bit of volume--if 80% of the volume under the cowling is floatation I feel like it's heading in the right direction and if the added width becomes foam there is additional gain. I am likely going to give it a little bit of a higher bow so the fore compartments could even gain some floatation to raise them a few inches above the deck level.

@bajansailor yes, free surface effect is something to think about and something I'm very much aware of since my inflatable spends much of its time half swamped and constantly onboarding water. I think stability tests with a wooden model will be particularly good for this consideration. One advantage to the skinny hull is that in our seas, a large volume water doesn't want to stay pressed up against side of the boat, it will funnel quickly fore and aft as the sea moves the boat, or g forces from the engine.

I can appreciate the catamaran design and would likely go that route on the next boat which may be more a family boat or if I was designing a recreational boat for myself, but I kind of like being swamped frequently. Our wetsuits are also VERY warm, which means when we're out of the water wearing them we tend to overheat, so it can be more pleasant to be constantly wet (not so much in February though!). Definitely not for everyone, and not all my students love my current boat set-up, but these are largely people who love being IN the sea so I have had many comment that they love being so close to the water. Small catamaran's do very well out here for serious bluewater hunting, like chasing schools of tuna in the open ocean a long way from shore, but that sort of thing is more consistent south of me by 50-100 miles, and to do it successfully takes an experienced team. Geographically, I'm set-up perfectly for island hopping. Putting spearos on bluefin tuna can be incredibly lucrative but again, it would be scaling up by some degrees of magnitude--location, crew, as well as boat, to say nothing of the experience required of the spearfishermen.

 

That could be a perfect mobile competition platform (although you'd want some kind of giant swim step type thing in case you needed to onboard an unconscious diver) and very comfortable for divers anywhere tropical but it would be pushed horribly by our afternoon wind and be much too big to be a dive float as I would use it. For what I want to do here it's use would be very limited. These are old spearfishing videos of me with my inflatable but you can see what I mean as for 'dive float'. The actual dive in the second video is 'very extreme' even by pro standards so with students I'm doing a much, much, much more tame version of this if at all, but maybe you can see what I'm talking about and some of what I want to do with the new boat design.

At the start of this video, before it becomes just dive clips, we're anchoring the inflatable on a pinnacle with a 25lb kettle bell and just 5% scope in the anchor line. I have to bullseye the target area with the anchor using GPS and fishfinder--we're trying to land it on an area which we cannot see from the surface, which is less than 1/2 the area of a tennis court and 35M deep:

Also, the sea conditions at the start of the video are for us uncommonly good.

This an actual dive on the spot, made a few years later, using the inflatable entirely as a dive float:

 

What is so damned frustrating is one minute he is free diving and doesn't want the boat to drift and the next minute, you are telling me he wants to swim it.

It can't be both.

The reason for the narrow hull is there is a floating barge in the berth and nothing more.

 

You could lower the bulwarks to zero and even reduce the hull height. The boats, at some point, are all affected by current. And two hulls are not subject to more wind than one; ftmp.

Those videos are cool. I'd not be able to do it. I'd get air anxiety; so really cool to watch. Are you not subject to the bends at 43M?

Mmmm..ling cod is really great fish..

 

He does two types of diving.

One record diving that requires a stationary platform.

The other is spear fishing which requires a mobile platform.

Twin hulls and current are not issues. As both swimmer and hull will be almost equally affected by current.

Freeboard that is blown while the swimming divers aren't blown is a major concern.

His proposed hull meets his sor. It may also be unsafe.

None of the alternative hull presented meet the sor.

Op can either build narrow and accept instability
Or
Wait decades for another slip to become available.

 

or he could be creative and build something that does both

 

Just a thought - if Socal's long thin boat does prove to be a tad wobbly at sea, he could always convert her into a proa with a single outrigger.

This occurred to me after looking at @Tiny Turnip fine collection of photos here
Around Jura by half https://www.flickr.com/photos/tinyturnip/albums/72157719822032375/with/51422335952/
showing a cruise around Jura (in the Scottish Hebrides) in a Solway Dory.
OK, this dory is essentially a trimaran, as she has two outriggers. But one should work well for Socal if need be, as he will only be under power (?)

 

If wind-drift is the main concern, then an out-size sea anchor would go a long way toward alleviating it, many offshore reef fisherman use them to slow down the drift, allowing more time over the spot, and being able to use less lead to get lines down. It can also be used to orientate the direction the boat is pointing, which could further reduce drift due to wind. It is a little bit of a nice problem as to whether a low profile boat is going to be superior as regards less drift, it depends also on the amount of boat that is under the water, and a very lightweight boat with little underwater profile might drift faster than, as as fast as, a higher but heavier boat.

 

So, the 25# kettle ball is the anchor for the rib. You can just as easily put out a 40# anchor for a larger craft, or use sabiki mode on autopilot, though some costs for that. The 18' boat he has drawn is still gonna drift more than the rib as well.

to reduce a drift; you can also water ballast the cat hulls; perhaps this is why he is talking about a wet boat, but you don't want the inside of the boat wet with saltwater all that much..especially when in the slip

 

re: wind and drifting
Sorry, this confusing. When doing ANY sort of spearing (swimming/divers) the boat is always either anchored or helmed. The ONLY time we are in the water with the boat just drifting is when we are training extremely deep for competition style diving, but we are in the water around the boat and in contact with it (ie not swimming away and just leaving it) the entire time. For extremely deep training/competition style freediving, the boat is NOT anchored and is drifting in the channel with 200' of dive line hanging off the bow of the boat with a heavy weight on the bottom of the line, and we're swimming up and down on the line. The weight is NOT an anchor in that case--it's meant to keep the line taught and vertical and for safety reasons must be well off the bottom. In that case the boat is a drifting dive float. This works for us because we nearly always have some kind of current but if EVERYTHING (boat, divers, and down line) are all drifting in the same current, then until we drift into the shallower water, the current doesn't matter to anyone in the water, our world is the boat (dive float) and line that we're following down and up. If we are diving on a stationary vertical line in a current, it gets very iffy to do these kind of dives because the current means the dives cost us more energy since our direction of force becomes diagonal instead of just straight down and up. When the boat is drifting like that though, if there is much wind, the boat will catch the wind and start to pull the lines and it's no longer vertical and we have the same problem as if the boat is anchored. We nearly always have some wind, but with my inflatable it's not enough to matter. Even a small RIB though has a much higher profile so it gets difficult to do this. Sea anchors do work up to a point (I have a friend in Hawaii that does deep training this way off a 22' RIB) but it's more stuff to rig and manage, more time and attention, and there are times and days when it's just impossible. He also needs a larger crew to do this.

re: heavy anchor
This is what is shown on the videos; I'm following a nearly straight line down to a target on the bottom. Bigger boats = more weight, etc, but especially in a current the anchor even though it's just a bell will always figure out how to get stuck somehow and it's a lot of work to get a 30lbs kettlebell out of a crack at 130' in a current on a breathhold. I don't want or need to go bigger.

I built my wood model at 14% scale (it's then 0.27% displacement of the real thing) and loaded her up pretty heavy to simulate a 230lb engine (balanced on the transom) and 600lbs of boat/fuel weight, and I put half that weight at the sheerline to make it a good deal less stable/higher COG than designed with seated occupants. Then I started putting 200lb (equivalent of course) shot bags on it. The driver offset heels the boat just a few degrees and when underway it would likely level out because a boat this narrow with that engine will be heeled to a certain extent by the motion of the prop (my inflatable does this with just 15hp). Loading 200lbs way off on one edge (first diver climbing into the boat) it certainly does heel but nowhere near enough to submerge the freeboard edge; if somebody is sitting at the helm when that happens then it heels a good deal less (as we'd expect, the boat gets more stable the more it's loaded). Divers seated on the deck against the edge, even crammed up against a single edge cause very little heeling. It is meant to be operated only with seated occupants; like my inflatable it would be challenging to stand up in it outside the harbor. It's possible to submerge the freeboard edge--one guy standing in the boat, leaning most of their weight out over the edge, with one guy balanced on the gunwale at the same time could submerge the freeboard edge if the boat is approaching its weight limit, but it would be quite athletic to balance on this boat like that. With 20 cubic feet of foam plus a hull that is inherently bouyant, it would be impossible for human cargo to actually submerge the boat unless we had a 8 people perched out of the water on the gunwales. One spearing friend asked, 'what about 2 x 2oo lbs men pulling a 200 lbs bluefin into the boat?'... I mean, that would be a lovely day but I think we'd figure it out. My buddies are so used to kayaks and boards they tend to instinctively self ballast in my inflatable but again, because the freeboard is so low it makes it easier to pull things into the boat and oneself into the boat; it's not like a high sided boat where to reach the water from inside the boat you're practically falling out of the boat.

One thing I also realized, the inflatable rights much, much more tenderly. The hard bottom will have similar stability but rights stiffly and will feel more tippy even though it's ultimate stability is comparable.

The wooden model I built also does not have a rear airboxes (which will increase stability some), or the fatty inwales which will also make it very difficult to submerge the freeboard edge.

And finally, if boat on execution just doesn't work out then external RIB style tubes can be added after the fact, in which case it would be nearly 100% idiot proof. The current design is NOT idiot proof but not meant to be.

 

You are failing testing 101 socal.

Your friends are supposed to be talking about two people helping a third into the boat.

When you test, you don't best case test; you worst case test.

Example.

The cockpit of my boat. I should have pushed the designer for a spec. Did not. My mistake. So, I did some planning just like you to determine whether a certain metal beam would work. Did the calcs and decided to build it. Cost was about $400.

Then I realized.. wow, what if three people load on it? So, me and my kid who were 400# combined sat on the beam. It sagged. Back to the drawing board. New one cost even more..

Anyhow, test worst case or don't bother.

 

There is worst case, and then idiot proof. Many of the proposed designs are idiot proof (ie the catamaran and outrigger designs).

My design is not idiot proof. A Zodiac is pretty much idiot proof. The freeboard of a Zodiac RIB also usually at least 24" on even a very small one. This freeboard of my design at the stern is about 14" depending on loading. If a conscious diver is unable to pull themselves, while highly bouyant in a wetsuit and possibly even wearing longfins, out of the water onto a 14" ledge sorry they aren't fit for the activity. There are maneuvers on the drawing provided labeled both 'idiot #1' and 'idiot #2'. The freeboard edge will submerge if a 200lbs idiot is attempting to pull another 200lbs idiot into the boat a certain way, but idiot #1 is really an idiot, I am not sure how he expects to pull his buddy into the boat like that, and if he sits on the edge like that boat starts to heel nearly 30 degrees and unless he has particularly good balance he is falling into the water before his buddy in the water even grabs his hand. He might get lucky and fall into the boat and land basically into the position labeled 'worst case ok,' and manage to get his buddy into the boat before submerging the freeboard edge or falling out, and if there are some non-idiots already in the boat and pressing themselves against the opposite edge of the boat idiot #1 can actually pull this off. Similar story with idiot #2. He has excellent balance to even stand on the edge of this boat in open water and he is most certainly throwing his back out when he heaves his buddy into the boat. These scenarios were not successful on my model, which is also less stable than my actual design, and they'd also require that the buddy in the water needing help is too stupid to realize that he should let go of the idiot in the boat to keep from tipping the boat over. Not shown would be 'not smart but not quite idiot' who is doing what 'idiot #2' is doing, but while kneeling. Boat is more stable that way, but to recap, I am not sure what idiot feels like they need to stand, balance on a tippy boat, and then lean down into the water and way over the edge to reach somebody in the water which is just 14" below the sheerline of the boat, all this from a deck that is a just a few inches above the waterline.

But, back to our idiots. If they manage to submerge the freeboard edge they are quite athletic to even get into the boat (after falling out, the boat instantly rights itself and drains), and if water enters and both idiots are in a swamped boat it's a swamped boat that just drains but slower since it has the two idiots providing some additional weight. If many idiots want to sit on each other's shoulders and perch on the gunwales they could perhaps eventually submerge all 1200 lbs of positive bouyancy provided by foam plus likely another 80lbs of positive bouyancy provided by the hull, but again, this is not an idiot proof design.

Worst case for me is an unconscious diver who is not responding to in water resuscitation. To heave somebody into a boat in which you realistically cannot stand on you would grab their wrist, put your butt down and feet against the hull and heave them in, labeled in the drawing 'worst case ok'. (incidentally that's how I pull that 30lb anchor into an inflatable in which it's not really possible stand, by using a pulley and my feet planted against the side of the boat) Boat is 100% stable this way and multiple divers can assist. I want to say the one time I helped somebody into my inflatable in all these years that's how we did it. Once or twice I had a really twiggy student with no upper body strength whatsoever (this complete lack of strength also means that they actually cannot swim well enough to perform the duck dive and get themselves underwater, so not my typical student) and being very twiggy and light the boyfriend would just shove them over the side from the water.

Back to the two guys, not idiots, heaving a 200 lbs tuna into the boat. I do know spearos who have had the good fortune to shoot the 200lbs blue fin on a 'proper' 16 foot center console then struggle to get it into the boat because they didn't have gaffs, etc. The freeboard of that boat is likely 36" so to reach the heavy fish you're hanging off the edge of the boat, half out of the boat to reach the fish, and on the RIB scenario somebody is freaking out about fish spines puncturing the tubes as it gets drug across the tube and into the boat . My freeboard will never be more than 16" at the stern end and deck is only inches above the waterline so no need to hang yourself half outside the boat over the edge to reach the water. And also, while I'd love to blast a 200lbs bluefin in this vessel it's not designed for that pursuit nor likely if island hopping.