Keels on flat bottom boats

[Orelious]

I have built a 8 m flat bottom boat it will be powered by an outboard
What size what length and where should the keel start and finish
????????

 

[Home Cookin']

Re: Keels on flat bottom boats

is it literally flat like a 24' barge? any deadrise at all? What's the bow shape? Did you build it without plans?

Some flat bottom boats like the Carolina Skiff J series, Skimmer and Bay Runner--and they are flat flat. The CS has chines about 1 1/2 inches deep all along the sides of the bottom. But they still slide, and then grab. Not good unless you are used to it.

 

[Texasmark]

Re: Keels on flat bottom boats

Like Cookin said, you need something to dig into the water when you turn. Otherwise you will just slide sideways. On welded alum boats, there is at least a 1" angle welded to the center of the boat covering the centerline weld where the two pieces of material that make up the bottom meet in the center.

If you have a wooden boat, I'd run at least a piece of 1x2 flat sided the full length of the bottom. If you want more, run another pair half way between the center line and the chine (area where the bottom meets the side), starting at the transom and running for 4' give or take. You don't need a big obtrusive keel like is on a displacement hull. Those things are there to accommodate and protect the prop.

If you ever water skied with a flat (trick) ski with no skeg, or tried to ride a disc with a flat bottom you know what we are talking about.

Mark

 

[Orelious]

Re: Keels on flat bottom boats

Like Cookin said, you need something to dig into the water when you turn. Otherwise you will just slide sideways. On welded alum boats, there is at least a 1" angle welded to the center of the boat covering the centerline weld where the two pieces of material that make up the bottom meet in the center.

If you have a wooden boat, I'd run at least a piece of 1x2 flat sided the full length of the bottom. If you want more, run another pair half way between the center line and the chine (area where the bottom meets the side), starting at the transom and running for 4' give or take. You don't need a big obtrusive keel like is on a displacement hull. Those things are there to accommodate and protect the prop.

If you ever water skied with a flat (trick) ski with no skeg, or tried to ride a disc with a flat bottom you know what we are talking about.

Mark

Thanks Mark good Common sense i was just a bit concerned about cavitation for the prop Thanks John T

 

[Orelious]

Re: Keels on flat bottom boats

is it literally flat like a 24' barge? any deadrise at all? What's the bow shape? Did you build it without plans?

Some flat bottom boats like the Carolina Skiff J series, Skimmer and Bay Runner--and they are flat flat. The CS has chines about 1 1/2 inches deep all along the sides of the bottom. But they still slide, and then grab. Not good unless you are used to it.

yeah Mate Build it without plans just out of my head Very little dead rise.. As I said to the previous guy I was just concerned it may cause cavitation for the out board

 

[Orelious]

Re: Keels on flat bottom boats

Thanks Mark good Common sense i was just a bit concerned about cavitation for the prop Thanks John T

Check the attachment

 

[roffey]

Re: Keels on flat bottom boats

Any pictures? Here in Canada we can only dream of boating this time of year. Think back to a happier time, when my boat was in my driveway calling my name and begging me to give her a ride, waite that was my out side voice.

 

[steelespike]

Re: Keels on flat bottom boats

Some flat bottoms have 4 or 5 keels to strengthen the bottom in place of more ribs/frames or heavier gauge.
You may just need a single keel to improve tracking and hold in turns.

 

[Texasmark]

Re: Keels on flat bottom boats

Thanks Mark good Common sense i was just a bit concerned about cavitation for the prop Thanks John T

The way you solve that problem is to taper it to the bottom about a foot forward of the transom. However, I have an alum boat that is welded out of 2 sheets of material joined at the center where a keel would be. After welding a piece of 1" alum. angle was placed over the weld and it goes from stem to stern. I may have a little prop disturbance from that but not much. If worried, use a cupped prop and forget about it.

Mark

 

[kfa4303]

Re: Keels on flat bottom boats

My tinny has a similar 1" keel own the center along with a few other "strakes (?)" on either side. While you may sacrifice a bit of draft, I think it helps the boat track in a straight line better as well as helping it to "bite" into the turns. It also helps to take a bit of the edge of the hull should you run aground, or hit a submerged object. Not that I've ever done that, of course

 

[Texasmark]

Re: Keels on flat bottom boats

Not that I've ever done that, of course

Is there a subliminal message here. Grin.

Mark

 

[kfa4303]

Re: Keels on flat bottom boats

Oh yeah, those oysters bars can jump out in front of you if you're not careful. That's when the tinny can take a licking and keep on ticking. I also find the keel helps to center the boat on the rollers on the trailer as well. Of course, a lot of guys down here obsess over every centimeter of draft, but +/- a couple inches isn't going to make or break me. I mostly just toodle around and look at the critters these days anyway.

 

[Home Cookin']

Re: Keels on flat bottom boats

keep in mind, to translate to merkin from strain,this is a 26' flat bottom boat, which I'd call a barge. Ones I know, called "lighters" and used in oystering, don't slide because they don't plane!