minimum speed required to plane

[salmonee]

Is there a minimum speed to get the boat to plane?

I recalled there was a big problem with the Larson I saw over the weekend getting it to plane at low speed. We were going against the wind, and the boat just seem back heavy with the nose pointing up until I gunned the thing. Is this normal? I wouldn't think so as I see boats slowly cruising at say 5mph.

 

[Mischief Managed]

Re: minimum speed required to plane

Yes. Planing speed varies by boat; and then by load, engine size, prop, trim and load balance. I doubt the one you saw at 5MPH was on plane, or not really going 5 MPH if it was on plane.

 

[abj87]

Re: minimum speed required to plane

Mines around 16-20 mph most boats should be similar. Some require damn near full throttle to get on a plane depending on the power it has. Mine jumps up quickly at 1/2 throttle but our friends 24 foot sea ray requires 3/4 to get up on a plane.

 

[salmonee]

Re: minimum speed required to plane

Yes. Planing speed varies by boat; and then by load, engine size, prop, trim and load balance. I doubt the one you saw at 5MPH was on plane, or not really going 5 MPH if it was on plane.

I meant can you cruise at 5mph with the boat being level. I'm wondering if the boat I test rode in was going against the wind and thus causing an upward force at the bow raising it? I tried playing with the trim but only speed would overcome the back heaviness of the boat. Trim was full down.

 

[mthieme]

Re: minimum speed required to plane

Doubtful.
Tunnel hulls and hydroplanes are design to channel the wind and lift the hull - but not at 5 mph. I can't think of anything that will plane at 5 mph.

 

[Mischief Managed]

Re: minimum speed required to plane

I meant can you cruise at 5mph with the boat being level. I'm wondering if the boat I test rode in was going against the wind and thus causing an upward force at the bow raising it? I tried playing with the trim but only speed would overcome the back heaviness of the boat. Trim was full down.

That's normal. Most boats have bow rise while transitioning onto plane. I doubt the wind had anything to do with it. Give it more or less gas to level it out. Trim tabs may be a good idea for the boat too, if it's typically hard to get on plane.

 

[tashasdaddy]

Re: minimum speed required to plane

boat usually do not plane under 15 mph, you have to give it enough power to get over the hump, then throttle back, but have to keep it on plane.

this is why it is said a boat motor is always going up hill, compared to an automotive engine that gets to coast down hill.

 

[Wee Hooker]

Re: minimum speed required to plane

As Tasshasdaddy said, most boats won't plane untill you get into the mid teens. (Some "displacement hulls" never plane at all but that's another topic.) The problem is that the boat has to climb over it's self created bow wave in order to "get up". In the mean time the bow wave push's up and back, making the boat squat. That said, you CAN travel @ 5mph with a somewhat level boat if it's trimmed correctly AND you go easy on the throttle. ( Think of fast tolling.) You won't be planeing but that's fine. She won't point at the moon until you attempt to attemppt to climb up onto /or fall off plane and have to deal with that bow wave.

 

[Ned L]

Re: minimum speed required to plane

Five knots (~6mph) is within hull speed of boats 15 ft and longer, so YES, at 5 mph your boat should be just about sitting on her lines, or "just about level". As to what speed it should get up on top & level off on a plane depends on too many things (hull shape, engine, # & location of people & gear on board, how clean is the bottom, how full the tanks are, etc), but if you want numbers, as has been said, somewhere between say 12 & 20 knots for most small boats (kind of like pulling a # off the side of a barn).

 

[Jdeagro]

Re: minimum speed required to plane

The boat is considered "on plane" when there is enough water pressure on the hull to lift the boat and allow it to ride on top. Since the bow area is lighter than the stern it rises out of the water first. Unfortunately this causes the stern to drop more and create a hill to climb before getting on plane (the Hole). Flat bottom boats plane at slower speeds than sharp "V" bottom boats because there is more surface area to lift the boat. As stated by others, most boats need to run at or near 20 MPH to maintain a level plane.

At slow speeds the boat will ride level until the speed increases and creates enough water pressure to lift the bow. Typically around 8 to 10 MPH. Bow rise can be as much as 17 degrees which will block forward vision.

Changing the hull design to give the stern more lift, and therefore keep the bow down (Stern down = Bow up and Stern up = Bow down), is the most effective way to achieve a more level ride at preplanning speeds. In short the hull needs a concave section (hook) in the hull at the back to create additional pressure to lift the stern. Since changing the hull is not much of an option the best solution is trim tabs.

 

[180shabah]

Re: minimum speed required to plane

A set of trim tabs will transform the way you boat handles. A great low cost option are SmartTabs. (I got your back John) They aren't helm adjustable, they are automatic, but they are a fraction of the cost of a traditional hydraulic setup.

 

[bowman316]

Re: minimum speed required to plane

Most boats have a hull speed of around 7 knots, or about 10 mph. Once you get over this, you start to climb up the bow wake, and get on plane.

 

[nlain]

Re: minimum speed required to plane

I will second the Smart Tabs, I have them on my boat and they are great, also have great support. Oh, and at the price of gasoline today if you boat a lot the will pay for themselves in gasoline savings.

 

[sickwilly]

Re: minimum speed required to plane

Prop pitch and number of blades will change the minimum plane speed.

Trim tabs (you can read here for hours on them, and clearly they are the best option) will get a boat planning at a slower speed.

Then there are a small minority of us outlaws that have a hydrofoil on our outdrive, which allows us to hold plane at slower speeds.


Why does it matter? If you have little ones that you want to pull skiing or are into wakeboardings, you need to be able to hold a plane at 16-18 MPH.

All IOs have a good bit of bow rise when starting out.

 

[QC]

Re: minimum speed required to plane

With my tabs full down my 23 footer with a 20 degree bottom planes at 11.5 MPH GPS . . . 17 MPH with the tabs up.

I have played with this a lot, for tubing and wakeboarding you can't beat either Smart Tabs or helm adjustable as they seem to stay put at a given (low) speed much better. As opposed to always increasing speed if you start at the point where she just starts to fall over (wakeboard speed).

As others have said, this is not about wind, so forget that. Even high powered boats need a good jam on the throttle to overcome bow rise without tabs. If you want to really understand the whole deal try bumping the throttle 100 RPM at a time. Ignore your dash speedo, especially below 20 MPH. GPS only. This exercise will teach you a lot about boat handling in general. From idle go to 700 RPM, watch what happens, feel it, give it 15 seconds to do what it's going to do. Do that for 800, 900 RPM etc. You'll find out that she will probably not plane until around 2500 - 3000 RPM depending on how long you wait between throttle bumps.

On the other hand, there is nothing wrong with mashing the throttle 100% until she pops up on plane (you'll know). Then immediately start backing off the throttle to select a comfortable (AND SAFE) cruise speed.

This whole balance of off plane/on plane, speeds etc. is part of the joy of learning this wonderful obsession. Whatever you do, DON'T cruise around other boats in that no man's land with your boat's bow stuck up in the air. A) your wake will pizz off everybody, B) you'll get terrible fuel economy there, probably the worst at any speed and most importantly, C) you'll look like an idiot . . .

 

[Tail_Gunner]

Re: minimum speed required to plane

Trim tab's actually help with creating a wake @ sub planeing speed's.. How do you do that leg in or out???

 

[QC]

Re: minimum speed required to plane

Yes, they can help build a wake as you can plane at lower speeds while alos digging a hole and then hold that speed better. A little hard to understand maybe but yea, I use different combinations of trim and tab depending on load and speed. Also, if I run with tabs full down it creates a rooster that will get tubers and wakeboarders wet, so I have to pull them up some. I have found the best spot is just when the little rooster settles down. If I use no tab, I have to go significantly faster and the wake starts to fall off. Without them I can get a decent wake too, if I constantly play with the throttle to keep her right where she just starts to fall over onto plane. Very hard to maitain that speed. With the tabs, the whole deal is more forgiving, adjustable and frankly fun for me.