When is your draft the deepest?

[Boatagain]

Our boats have semi-displacement hulls, correct? I was wondering when there's more boat under the water, at displacement speed or planing speed, all other things being equal.

I always thought that when the boat lifts up on plane, the draft is shallower, but the service manager at my dealer says the opposite is true. To ask this question from a more practical standpoint, say you unavoidably find yourself in shallow water, which speed condition would provide the most cushion against scraping the bottom? Of course, I'd rather hit bottom, if bottom is going to be hit, at a slower speed, but can getting on plane raise the boat enough to make a difference?

 

[Stevan47]

Hi Boatagain: I cannot comprehensively answer all your question/s on this topic, however just out of interest it may be helpful to know that when underway in shallow water, for example when there is around a metre or so under the keel, anything above about 8 - 10 knots will cause your vessel to sink a little deeper. This is called 'shallow water effect' and what happens is the planing effect of your hull travelling through the water, combined with the proximity of the seabed (earth's surface), results in a suction effect, drawing your hull deeper. Nothing too drastic to worry about, but worth bearing in mind if you are in really shallow water and wish to increase speed. The suction naturally has a slowing effect on the vessel's speed. If you already knew this, well and good. If not, all good information to store in the brain! Kind regards

 

[Irish Mist]

I would say if you were in a bass boat on plane going fast you would be drawing less water then going slow. My tug does not plane in the sense of getting up on the step When it is going it's fastest it is drawing more water in my opinion then hull speed .

 

[walldog]

If you are in depths where a couple of inches will make a difference, dead slow is best......trust me on that. Luckily my experience was in soft sand at 17 knots. Coming to a dead stop instantly is hard on your body and the loose items in your boat.

Also since Ranger Tug puts the transducer for the depth finder at the stern of the boat, you get better depth indication if the water under the transducer is calm or does not have a lot of turbulence under it as it would have if you were trying to get on the plane.

 

[PhilR]

If I'm in sandy bottom, I put trim tabs all the way down and go just fast enough to get some lift. Does it work? I don't know, but it seems like a good idea.

Phil

 

[NorthernFocus]

I've never really measured draft but my displacement maxes out around New year. Though draft likely doesn't change due to the increase in beam.