Flat Bow?

Hmmm. I keep seeing plans for boats that are capable of off-shore work that have flat bows rather than coming to a point. For instance, the larger Bolger Advanced Sharpies are like this.

Since the bow is above the water line, I can see that it will not need to cut through calm waters, but waters are often not all that calm. None of my design books show a flat bow of this nature.

Can anyone comment on the nature of the flat bow from a design perspective? I like the idea of shortening the overall length of the boat, having more room to work anchors at the bow, etc. but wonder about the safety.

Many Thanks,
- John

 

'Flat bows' , generally known as pram bows (and the flat of the bow is known as a transom just like the stern, only differentiated by 'bow' transom), are a very interesting design solution, much under appreciated of late.

It gives more 'boat' for a given length, more deck space, volume and greatly increases righting moments.
A pram bow means you can reduce beam and still have the same righting moment.

As to it butting into waves...Everyone wonders about this.
Well it is not nearly as bad as you might think, because the tremendous reserve of buoyancy does not allow to bow to sink into any wave, instead it lifts over them. However , in very short chop it can indeed produce very spectacular splash because the wave is too short to allow the boat to respond.
Of course just as in any boat it is very important to keep all weight out of the ends.

 

If you want to take a shoe box shape off shore then don't try to sail around much with it, you'll just wish you'd shaped it like 99% of the other boats out there. There's a fairly good reason we make the pointy end go at the front of the boat, which is especially true of ocean going vessels.

The pram bow is reserved for barges, scows and a few other craft, but even the most lowly of vessels will have a conventionally shaped bow, because they expect to maneuver, cost less to build, get through the water with a minimum of fuss, would prefer reasonable fuel efficiency, etc. The list is rather long in favor of the pointy end being at the front of the boat.

On the other hand, if you just need a diving platform or similar limited role vessel, then the pram bow is an option.

When selecting a design it's often best to not look at specific designs or design elements (like bow types) and focus solely on what you need a boat to be and to do. With a well defined list of goals, the hull type will usually present itself as an obvious choice. This is especially true of those that don't have an in depth comprehension of the subtle arts in yacht design.

 

I sometimes run 120 to 140 ft landing craft with a single gate. The sea often dictates where I can go because of this flat front (even tho the flat starts about 6' above the waterline).
Last year, some folks built a nice, new aluminum boat with a gate (popular up here for dropping four-wheelers off on a beach and such). They had huge horsepower and thought that, like with their old boat, they could minimize time spent in a tourboat wake by jumping it at what appeared to be 40 knots.
You know where the rest of this is going (they survived and idled home) but it was one of the most violent instances I have ever witnessed on the ocean. The spray (some of it was solid water) made a perfect fan about 120' radius. I knew it was going to happen about two seconds in advance but did not have time to get it on film...

 

Tcubed - Thanks for cluing me in on the name of the design. That helps a lot. It also helps to know about the extra stability and other technical thoughts.

Par - you are great as always and are really appreciated around here. I should have mentioned our plans: This is to be a family home on water. We've found that 90% of the time or more cruisers are anchored, on the hard, or docked. 3% or so of the time they are off shore. We need to be able to go off shore to make passages but not for months on end. We need space for a growing family and a lot of weight. If the winds turn against us or we spend a lot of time some place like Puget Sound, then we need to be able to go to windward when necessary and not overly suffer. We could care less about a real race other than seeing who gets to the next anchorage first just for kicks and bragging rights - not going around bouys. We don't plan to take on cruising though ice but most anything else is probably going to happen. All of that said, we have been thinking about a sailing dory or other type of flattie. We can get a lot more room in there with these designs, stay shallow on the draft, still get to windward ok, etc. Building it will be a lot more simple for the family too. Where Tcubed was specific about what we might find with a pram bow, can you offer up what we might encounter in different conditions? Can you also say why the sharper bows are better (or worse) in those cases so that we can evaluate if we want it on our boat? The current design we are looking at is a motor sailor of 42-48 feet LOA, 5' wide transom bow that is 2.5' off the water, and has enough sail to be considered purely a sailboat if we can't always afford to add iron thrust. Any additional comments you make will be greatly, as always, appreciated!

Mark775 - Thanks to you too! How would you suggest your friends had handled that situation? Is crossing wake or a rough bar different with a pram bow?

 

I would like to remind our readers that most of the Chinese junks were prams.
There were inshore junks and there were ocean going junks (also prams) also, some of which ended up making rather epic voyages.
My father recounted how several sailed past him when we were there and he was very impressed with how well they sailed.

So pram bows can certainly perform allright and be seaworthy, provided of course that the design is well and intelligently executed.

________

I used to have a 22 foot scow with leeboards. It was a Howard Chapelle design. I was impressed by how well the thing went to windward almost never pounding. This is like i said because of the large amount of reserve buoyancy, but also because when heeled, it would be riding on the chine , so to speak, and thus become effectively a v bottom boat.
________

Also the bow transom can take on any reasonable shape, as well as angle.
The boat may be round hull, hard chine, etc. The possibilities are endless.

So i would not comment on the dimensions you mentioned without looking more closely at what your list of objectives and priorites are , as well as approaching the design from a more holistic standpoint. There is no point deciding what design features you want before having a very clear idea as to what will be required of the boat, from build to use.

 

LOL, Mark you stole my Thunder.
Lots of Landing craft in AK.
Some times you load up and have to wait for a day or two for the Sea to flatten out.
Down in South East AK, we pretty much ignored the weather and took Jeeps, etc out to the islands. You actually want a pretty high sea to make sure the cargo don't drowned on the landing.

I fish out of small rowing boats. I want a 'jon' boat which has the Front transom. I want the flat hull in front to offset my lack of balance.

But I still get 'thumped' pretty good by that front transom if the distance between large waves is short.
It's just water.

 

So if the wave frequency is close,the pram bow is problematic. BUT the length of the boat will play into that scenario. An Opti, or similar,could negotiate short wave patterns better than a longer boat, right? Also speed must play into the wave encountering dilemma. Boat direction with respect to the direction of the wave travel too.

A simple question can, and often does, turn into a series of ifs, ands, and maybes. That is the stuff by which we boatniks seem to be mesmerised.

 

Well, even with the boats Mark drives, a wave will tend to lift the boat ahead of the crest of the wave at times.

You can take a small Jon boat out and experiment with that wave action and the 'bump' you get when the bow goes over the top of one wave and crashes right into the oncoming wave.
Measure the waves. Vary your speed, and you'll have the answers to all your questions.

 

You can screw around with drive speed, how to approach waves, how much stouter you have to make the forward sections of the craft, etc., etc., etc., all so you can have a pram bow, or you can stop fooling around with foolishness and use a conventional bow.

Again, there are several good reasons we stick the pointy end on the front of the boat. If you're finding difficulty justifying its use, then might I suggest some books on engineering and yacht design. Do you really think we'd incorporate the difficult shapes used on the front of a commercial ship, bulbous bow and all if we could get by with a simple slab of pram bow? Please, reinventing the wheel without know what makes it go 'around is folly on the highest order.

Yes, there are pram bows in use, but quite literally a small fraction of a single percent of ocean going craft incorporate them. This is a clue, take it.

 

PAR cut through the fat with the 'pointy end in front' thing.

On a troop ship headed to Korea we ran into a Hurricane at sea.
That ship'd dive into those waves deep and the boat would shudder as the props came out of the water when the wave went by.
The Bow would still be coming up from beneath the sea.
The pointy end was still stuck under a big wave and the stern was stuck up in the air over a hole in the ocean.

But the ship was still going forward.
If the front had been flat, who knows where the stress would have escaped from.
You'd expect the sides of the ship to buckle when the pointy end dived deep down and stopped in the water, while the rest of the boat was still coming on.
Sometimes it did. My bunk was near a seam in the boat and I'd get sprayed every once in awhile.

You cant hit a wall of water with the flat end of a boat and not expect some spectacular events.

But PAR, the reason I want a Jon boat, flat up front, is so I can lean back when rowing, and not have the pointy front end try to get out from under my bulk.
It tips on me when I do that.

 

I've been through this place myself. Taking a common sense to this question, my instinct was to ask how many times a sharp bow actually gets to fulfill it's intended purpose, i.e., cutting through water. One answer that fits all cases is "it depends".

If your boat is used in more or less flat water conditions, a small lake, typical estuary or suchlike then the answer is, it likely won't get wet too often and might as well be hacked off. This is pointless however unless there's some profit to it, the ability to fit a bigger boat into the same space perhaps, or the extra buoyancy at the bows can be put to use.

However, it isn't simply a case of hacking off the sharp end. The bow transom does not have to be vertical, for a start. The bottom shape of pram dinghies is usually different, lots of rocker being one obvious thing, helps keep the blunt bow well clear of the water in wave conditions. Unlike a pure rowing pram, a sailing pram has to accommodate heeling and the tendency for the thrust on the sail to push down the bow. And then there's outboards ...

Therefore with most pram designs it's not just a question of losing the pointless sharp end (sorry - couldn't resist), a set of compromises comes along with that will impact on performance and under some conditions, comfort.

Having said all that, I although I considered a pram design for some time, I eventually chose a conventional bow (one of PAR's designs actually) partly because it was easier to build, as I have found transoms are a bit harder to do than stems, and partly because it just looked so damn nice. It's not always a logical choice, you see ...