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30' Sport Fisherman   Boat building project

design and build of a center console offshore sportfishing boat 


Computer Design





The Design

This was my first design an it wasn't too before I saw the need to organize the design process. I developed my own way of simplifying the design by breaking the hull bottom down into three parts, the entry, the transition and the running surface. Looking at the hull form the side view, this would the front, middle and the back. The running surface is the simplest of my boat and that is where I started. Then I further broke the hull down into the bottom and top sides. Since ride was my main concern The bottom design was worked out first.

The Running surface. This starts at the transom and runs forward about 8 feet on this boat. This is simple because it is a constant deadrise and width. Basically the hull bottom sections are identical. As typical in many of these type boats, these are flat, no curves and I choose 25.5 degrees as my deadrise at the transom and running surface. I went a little overboard here thinking the boat would be lighter than it turned out and the full length keel lift pad would add back some lift that was taken away by the 25.5 deadrise. The next thing I worked out was the entry.

The Entry. Two main objectives here were a sharp vee, 60 degrees was my target, and the pronounced upward curving stem line that started about mid ships. The look that I wanted was when you looked at the stem line from the side, the leading edge of the stem would run at about a 45  degree angle in the area of the entry and more of less continues at the angle to the forward tip. Thus the actual  entry would be quite a distance above the bottom line of the hull. This is the essence of the "South Florida" look. This opposed to the "Carolina" look that also has a sharp entry but the stem line would be more in the range of 60 degree and might even get to around 80 degrees near the forward tip. I was targeting 60 degrees as the vee that I wanted but it is only about 55 as  60 degrees was hard to hit as other things were being juggled around. Next you might expect the transition section of the hull to be just an afterthought and just connects the running surface to the entry. This turned out to be where I fiddled around quite a bit.

The transition. With the upward curving stem that I choose, the entry is taken out of the picture when you going into a 2 foot or so wave as the entry would pass over that size without hitting it. This size wave and smaller hits the transition area. This is where "fat cheeks" are not helpful to the ride. If you are motoring along at 20-25 mph then not so much of an issue but as you go faster, up in the 40-50 range then that transition area is actually functioning as the entry. If you look at the hull of any boat, notice the chine about 1/3 of the way aft from the bow. Say, if you were looking at the typical 24 degree "deep vee' hull the chine in this area is not so much elevated or curved upward from the chine at the transom and running surface. In an instant you can deduce that the boat you are looking at has "fat cheeks". Next look at a true "South Florida" look hull and you see a much elevated chine at the same point. Weather of not the stem line follows the classic South Florida curve, this is the most important thing a fast boat must have IMHO.

A lot of other bs. There is the forward buoyancy issues and trying to make the hull from the chine down work with the hull side shape from chine to shear, and the looks here is no small matter. It has to be pretty. A high bow with flair and upward curved shear that is usually missing on the south Florida style are some of the things that were must's for me. This is sort of an overview of the process and some of the objectives that drove the design.


My fishing objective is running out to deep water and sometimes this involves a  "game Plan" change such as running to a new location. As far as fishing in a small boat, I don't think there is a lot you can do with the hull design except maybe a relatively high bow might reduce taking waves over the bow. Stability at rest or at slow speed will be compromised by a bottom design for running. 

For the running part, I want to go relatively fast in normal Gulf of Mexico seas off  my home state, Louisiana i.e. 2-3 foot chop and occasionally somewhat worse. This is an overriding consideration that is to be accomplished at the expense of other things such as; floor space, stability at rest, inlet running ability and speed+fuel efficiency in smooth water.

It was my opinion based no almost no actual experience, that small "runabout/fishing" boats do not require a naval architect for a successful design. Armed with this lightning bolt from above, I proceeded with my design.

First I considered what made my existing boat, a 24' SeaBird, a successful design. It's cored hull is light, it has a 24 degree dead rise, it has the "South Florida" curve to it's stem line and it's narrow.
Next I tried several demo's of hull design software. HullForm 7G was the only one that I could easily make something that looked like a boat. Bought it. I  developed a "table of offsets" from my SeaBird that I entered into the computer as a starting point.
Over the period of a year or so, I designed the hull over and over as I looked at lots of boats and my thoughts progressed. Some of the boats that I admire are;
              Contender 27' and 31' (overall design and appearance
              Regulator 26' ( classic shear line and bow flair)
              Fountain Sportfish 29' and 31' ( bottom design)

Deep Vee, Sharp Entry, Light Weight, Narrow Beam

What I ended up with was a 29' 91/2" LOA hull , including the integral motor bracket. The dead rise at the transom is 25.5 degrees and the entry  dead rise is 55+ degrees. The is hull is narrow at just a little under 7' beam at the water line. The hull topsides flare out over it's length to a maximum beam of 8' 6" gunnel to gunnel at amidships with a noticeable bow flair. The amount of dead rise is pushing the idea of deep vee a little far but I thought that the hull's lightness (projected weight at 3600#) would offset the loss of planning lift and buoyancy from the steeply angled bottom. There are some other handling and stability at rest issues that may have been compromised but these are some of the trade-offs in aiming for a special purpose boat rather than a general purpose boat.  The planning lift issue was to be addressed with the 16" wide keel pad that is set at 12 degrees dead rise and the other hull bottom appurtenances.  The bow stem line lacks the usual "Carolina Inlet Running" curve that is found in some degree in almost all production fishing boats of this size and favors the " South Florida " style curved stem mostly found now only in custom or semi-custom boats. The ample forward buoyancy of the Carolina style is hard to argue with for running inlets and large swells but we don't have those conditions here that often. My old SeaBird told me that the south Florida style does nicely in 2-3' seas. In trying to explain why is where I get a little shaky in my boat design knowledge , I should save myself the embarrassment and stop here, but here's what I think.  In rougher situations where you are running with the bow trimmed down,  moving the forward planning surface more to aft by having the hull starting its upward slope (stem curve) further aft reduces the planning lift leverage of the bow or entry. By doing this, the bow rise upon entry into a swell, is less due to the bow's reduced leverage and also less leverage allows the bow to start falling sooner after exiting the swell. I admit this a simplistic explanation and you could talk about how the center of planning lift changes as swells are encountered and so on, but I have ridden in a number of "deep vee" hulls at some considerable speed in all sorts of the sea conditions that are typical to the northern Gulf of Mexico. In some boats I might have felt the ride was most affected by the excessive bow rise, in another's the bow drop was too abrupt with a lurching forward feel. In another there was an "impact" that noticably slowed the boat when a swell was hit. I picture the hull attitude on a Carolina Style boat maintaining its running attitude slightly longer thus making the eventual drop off the wave more abrupt. And when the bow contacts the next wave it is lifted more. When the Carolina style boat hits a large wave at speed there is a big impact as the broad shoulder ("fat cheeks") of the hulls forward area tries cut though. This may be full of holes but there is a real difference in the feel of the two styles and this is the only way I can explain it.  Anyway, After I finished my design, I noticed a picture of a 34' Venture and the upward swept chines indicating a very sharp entry vee and South Florida style stem curve. After a phone conversation with them I felt much better about my design. For those unfamiliar with the Venture, It is a VERY nice boat but a little bigger than my tailoring requirements. Lately, I have noticed a few more boats with the sharp entry and transition area starting a little further aft than norm. In order to gain some of my "insights" I gained a reputation of being a little crazy. I mean this wasn't a science experiment and after a while I noticed I was getting shorter in height. The waves were trying to keep me away from the fish, so I just looked past them, I guess. Crew members didn't always see it my way! But what I am saying, I think, is when you ride in a hull that was too much bow rise and another where there was too much drop and they both have 24 degree deadrise, you realize the ride is not all determined by the transom deadrise and maybe, the most important of all, there is no ideal design that fits every situation. While on this rant, I would like to point out the catamaran that is supposed to be all conquering is great, but the Glacial Bay cruise speed of 27-28 mph is different than trying to go 40+ mph in a deep vee. The GB barely even goes that fast and when it does, it's ride gets really crazy. Again, it's about the compromise that boats are. The famed 31' Bertram ride may not be so great at 45+ mph? I know it can go that fast and even faster as ole Dick famously proved. But his ass was "on" the transom, literally, and speed was the only object. That is not the same as the 31' you see at the marina! I am not saying my design is some sort of optimum but it does work as I intended, it was successful to that extent. Put differently, it's particular compromises are a blend that met my goals. Another variable is our location in the Northern Gulf of Mexico, our waves have their own characteristics that work well with some designs and not with others. Anyway, I was trying to explain what I perceived as differences in the "South Florida" and "Carolina" entry styles. I must clarify what "Carolina" style I am referring to. I am speaking about mostly center console fishing boats say 24-35 foot lengths. These are boats like Regulator Marine, Hydra-Sports, Wellcraft Coastal and Fisherman. These all have the stem curve starting in, what might look to most, as the "normal" area. The South Florida style is boats like the Venture, Wellcraft Scarab, Donzi and my old Seabird for example. I definitely am not talking about Carolina styled sportfishermen's like the Buddy Davis and the like. These are very different hull designs than what I am discussing.


Motor Mania

The original design was started  for a jack shaft inboard/outboard  diesel. The engine selected was the Star Power  7.3L 300 hp turbo diesel with matching outdrive. The engine was located under the leaning post/tackle center. Eventually I soured on that setup in favor of twin, just introduced, direct injection 2 cycle outboard motors. Again there were some trade offs here, but it seems the greatest thing in the diesels favor was the fuel efficiency and the direct injection outboards appeared to gain some ground in that area. That was before all the trouble started with both Mercury and OMC versions of this new technology. Since then with the OMC bankruptcy I am very glad I choice the Mercury Optimax. A consideration was trolling speed. With the diesel propped out for this light boat even at idle, the troll speed might have been too high. Star Power had a two speed transmission under consideration but there was no way to know if this would end up being available to me or how much it would add to the already steep price. The hull was being built and the transom had to be cut for one or the other. As it turns out, had I chosen the Starpower unit, it would have been a big mistake because in the intervening year their engine/outdrive package was discontinued. 

Looks are important too

I have always admired the classic gracefully curved shear line that the "Carolina" boats use to accommodate their higher bows ( example,  Regulator ). Although I did not follow the Carolina style stem curve, I did made the bow high and tried to get that classic curved shear look. Since I am building a linerless boat with hull cap ("covering boards") integral with the hull, I could  style their widths for fishing ease and looks. I started a little wide at the rear (9") and got very wide forward(14"). The forward width gives added safety for boarding and can easily accommodate outward pointed gunnel rod holders for fishing and quickly getting cleared rods in a safe out of the way place with hooks hanging overboard. The bow flair was important part of the looks package as well as hopefully keeping some of the water out of our faces.


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Last modified: November 09, 2015