Low speed at deep waters

[Ledif7]

I have a 100 HP and a 17 ft 3 hull boat (catamaram) I was driving it in a channel and the speed was fantastic. Very fast. Once I got in braoder, deeper waters it seems like tha boat lost lot of speed. It seems like was running very slow. Is that normal?

 

[Trent]

Re: Low speed at deep waters

Need more info please..Was it shaking, sputtering or running the same???????????????<br /><br />What make, model and year??????

 

[CAPTBLACKSMARINE]

Re: Low speed at deep waters

IT WAS YOUR IMAGINATION. OR NO MORE THAN COINCIDENCE AT THE MOST .WATER DEPTH HAS NOTHING TO DO WITH HOW YOUR BOAT RUNS,SO LONG AS YOU DON'T RUN A GROUND. WHY DID YOU THINK THE BOAT WAS GOING SLOWER? MAYBE IT WAS ,BUT IF SO IT WAS BECAUSE OF SOMETHING ON THE ENGINE NOT BEING RIGHT NOT THE WATER.

 

[Ledif7]

Re: Low speed at deep waters

I noticed it because of the feeling you get when you are running at high speed. In shallow water I felt like I had to hold myself for not going backward.You know the speed rush. In deeper waters I felt like I was standing the same place, more or less. Once I move back to shallow waters I got back the feeling I have to hold myself. Got the idea?

 

[CAPTBLACKSMARINE]

Re: Low speed at deep waters

YEA IT WAS YOUR IMAGINATION . GO BUY YOU A TACHOMETER AND SEE IT FOR YOUR SELF.

 

[f_inscreenname]

Re: Low speed at deep waters

At WOT even the smallest wave will slow you down it just depends to what degree. It sounds like your boat likes clean water. Tri-hulls builds a air pocket under the boat to lift them (chopy water,less air).

 

[Walter]

Re: Low speed at deep waters

I've always wondered why my boat gets such good gas mileage on the first half of the tank, but goes through the second half tank in nothing flat.<br /><br /> Walt

 

[ICEMAN]

Re: Low speed at deep waters

Hi, Personally I don't like the way some catamarans ride. Imagination????? What about the current in the waters you ride in, Current will have an effect on the boat, Maybe it is in your case, maybe it's not. If you can give a little more info it might help. When you go thru the channel, I guess your going a little slower, then when you hit deeper water you increase speed. Is this correct? Does it feel as if the engine goes faster, but the boat does not?

 

[ralph]

Re: Low speed at deep waters

You may have been experiencing "ground effect" A boat will tend to plane with less power and slower speeds in shallow water since the water is "compressed" under the boat. The water must be under two feet for this effect to be noticeable.

 

[DJ]

Re: Low speed at deep waters

I'm confused. Water does NOT compress. Try putting some in your engine and turning it over. You'll prove it to yourself. Just kidding don't do it.<br /><br />Trust your instruments. Just like pilots. Airspeed is airspeed. However, when you're real close the ground it appears you are really going as opposed to 10,000 feet-it seems like you're crawling.

 

[araiha]

Re: Low speed at deep waters

Water depth does affect speed. It does several different things, although in general shallow water will slow you down not speed you up. My boat 'feels the bottom' at about 4 feet of water. It will feel sluggish and (particularly while in displacement mode) will make a bigger wake.<br /><br />Most of these effects are for displacement craft.

 

[wakatoa]

Re: Low speed at deep waters

Boats and ships will do all sorts weird things in shallow water. I have driven a large jet boat that went much faster in about 2 feet of water than it would in deeper water also a twin screw disp boat that made a hideous noise with lots of vibration when driven at speed thru shallow water (not intenionally)- look up 'canal effect' some books or sites will have a good explanation.

 

[DJ]

Re: Low speed at deep waters

I can see driving boats at displacement speeds through shallow water having an effect. It's not because the water is compressing. It's because you are pushing huge amounts of water ahead of you and out to the sides. That pushed water is hitting something-the bottom or the sides of a canal. Thus the canal effect. Your wake will be larger in a confined area. Sort of like sticking your hand in a full glass of water. Guess what, you spill a bunch.<br /><br />Water does not compress. It has to have someplace to go. In deep water there is room for the wave action created by displacement speeds to disperse.

 

[ebbtide176]

Re: Low speed at deep waters

 

[johnk@olg.com]

Re: Low speed at deep waters

At displacement speeds, shallow water can slow you down. i used to see this a lot in my grandfathers 28-ft Verity Skiff. It was like the boat was getting sucked down towards the bottom. The stern would squat, the water would pile up behind the transom more and the wake pattern would change dramatically - a lot more shallow 'V' behind the boat. <br /><br />But in my 13' duck boat, I purposely ride along the edge of the sand bars to get the sucker up on a plane. With me, a buddy and a full load of gear, the outboard can't plane it unless i get in shallow water. Get out in the deep, and she slows down and comes off the the plane. <br /><br />With a 17 ft boat planed off, I would guess that you would have to get in water shallower than about 4 or 5 ft before you would notice any increase in speed from the shallow water.

 

[Ledif7]

Re: Low speed at deep waters

Well thanks for the suggestion. I guess the best way to see if it really happens is to buy a speedometer, the one I have is broken. I will keep you posted on the results.

 

[Franki]

Re: Low speed at deep waters

I have been thinking about this..<br /><br />When I was studying hydrolics at uni, (fluid mechanics actually) we learned that there is actually friction between liquid and the pipe it runs in, so the fluid at the center of the pipe will travel measurably faster then the liquid at the outside of the pipe.<br /><br />Now that same theory would play with shallow/deep water as well, if you are displacing alot of water with your hull/hulls then that water is moving slower in shallow water then it would in deep.<br /><br />meaning you'd probably move slower in shallow water.. (although fairly marginal.)<br /><br />it would also make sense, that if the water was moving slower, you would come to plane faster as the boat would be pushed up onto the slower moving water as opposed to pushing it out of the way...<br /><br />and once you are planeing, you are not displacing anywhere near as much water, and so you'd go faster.<br /><br />makes sense if you think about it.<br /><br /><br />rgds<br /><br />Frank

 

[steve forsythe]

Re: Low speed at deep waters

Here's my 2 cents. You ever ride in a car that is real close to the ground compared to a truck? Same speeds feel faster closer to the ground, right? The closer to the ground you are when you are moving the faster it feels. Getting on a highway doing 60 on the on ramp in a SUV and then do 60 in a Corvette, the Corv. feels much faster being real close to the ground. I believe the same effect happens in shallow water. You can "see" the bottom or clear water moving under you, thus 'feeling' fatser.

 

[grandx]

Re: Low speed at deep waters

My opinion, it is your imagination (optical illusion). Any effect of fluid hydraulics in shallow Vs. deep water are probably not appreciable, the fact is the water moving against the hull (deep or shallow) has the same friction. Wave height, period, wind, and currents from deep to shallow water will effect speed. If you can find similar conditions in shallow and deep water on the same day, take a gps and note speed at equivalent RPM and let us know what you find.

 

[novacane]

Re: Low speed at deep waters

heres my 5 cents its like jumping in my shallow go cart @50mph vs my van @ 50mph same speed just that feel is way differant and yes water can not be compressed ask my diesel customer when he drove his diesel pwred oldsmoble through a 2.5 foot flood lol