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PostPosted: 13 Jul 2016, 10:14 

Joined: 29 Jun 2016, 10:12
Posts: 21
Hi there, in my last post I explained that I'm a complete newbie but really want to learn the correct way rather than being one of those boaters everyone looks at like "they don't know what there doing"
I was hoping that some one can fully explain what planing is. I have obviously read Wikipedia and I understand the concept of hydrodynamic lift but if some one can can explain it to me in terms of my 12 ally v hull lightweight that would be great.
Also I'd like advice on weight distribution. When I'm on the boat on my own the front lifts considered making it hard to see. When with friends it seams good but if I have some one sitting right at the front we get a lot of splash. Where should the weight ideally be centred baring in mind obviously me the motor and fuel will always be at the rear.
As I said rookie questions but I'm learning.
Thanks a lot


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PostPosted: 13 Jul 2016, 10:28 
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Joined: 25 Jul 2013, 16:12
Posts: 618
Location: Contoocook, NH
What is the boat and motor?



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PostPosted: 13 Jul 2016, 10:45 

Joined: 29 Jun 2016, 10:12
Posts: 21
It's a Czech built (I'm in the uk) called a marine 12m and I'm using at the moment 4hp Mercury 4stroke but will soon up grade to a 9-10hp in the new future. Out board without a console. The boat alone only weighs 65kg and I'm a skinny runt too ;)
Tganks


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PostPosted: 13 Jul 2016, 10:46 

Joined: 29 Jun 2016, 10:12
Posts: 21
It's a Czech built (I'm in the uk) called a marine 12m and I'm using at the moment 4hp Mercury 4stroke but will soon up grade to a 9-10hp in the new future. Out board without a console. The boat alone only weighs 65kg and I'm a skinny runt too ;)
Tganks


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PostPosted: 13 Jul 2016, 12:20 
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Joined: 12 Dec 2014, 14:32
Posts: 1559
Location: New England
Ahoy mate, from across the pond!

"Planing' is quite simply the hull running on TOP of the water (see attached picture) whereas at slow speeds the hull is IN the water and operating at what is called its 'displacement' condition, think of BIG ships like oil tankers. There is a limiting factor in just how fast one can push a vessel at displacement speeds, regardless of how much horsepower you put behind it. A British nautical engineer devised the formula back in the 1800s, where they proved that a hull cannot travel any faster than the bow wave she creates and the speed of that wave is 1.34 X the square root of waterline length. That 'bow wave' phenomenon is why you'll see those bulbous projections going forward and under water off the front of big ships ... to break up that bow wave from forming. Personally, I find this kind of stuff absolutely fascinating!

For you, think that to go fast, you need to get your boat up and out of the water, well at least the forward portion anyway. And to get out of the water, the bow has to rise ... but as you're experiencing, sometimes that bow rising can impede your view forward. It can also be dangerous too. And know that trim (weight distribution forward to aft) is super critical on a small boat, especially where the OB trim is usually fixed by the OB angle trim pin.

Options for proper trim - (1) Move the load carried, (2) change the OB pin trim angle, (3) add a hydrofoil to the OB vent plate, or (4) add Smart-Tabs.

Easiest is option #1. I once had a boat where I put on a long enough fuel line so I could put the tank back near me or way up in the bow when running alone.

Option #2 can be a pain in the arse to change all time, never mind you could drop it overboard, but try it. I had a boat and OB horsepower combination (every rig/combo IS different!) where no amount of load distribution would help and this was before i knew of hydrofoils. I had to move the pin to one position whilst alone, and then another when carrying a load or 2 or more people.

On small boats I hesitate to carry someone in the bow. Besides the spray, the small boats just don't have the power or oompphhhh to get and keep the bow up high with low HP motors ... and you only have a 4hp.

Option #3 foils are quite controversial - 3 schools of thought, those that love them, those that hate them and those that never tried one. Personally I'm a fan, as there are advantages to them, as they can add significantly stability and safety to a small boat otherwise. But they do rob you of a few MPH or KPH on your potential top speed, but I never run my OBs flat our wide open RPMs anyway, but for a few minutes each outing.

Per actual boat testing, the best out there (minimizing speed loss) are the ones by SE Sport, that you can look up. I actually have an SE Sport 200 I'd give you if you paid the Royal Post shipping charges, but there's no way I'd add one to a 4hp motor! About 20hp will be my recommended minimum before I'd consider one.

Option #4 Smart Tabs have been used successfully by many fellow tin boaters on this site, like that from Richg99. I never had considered them, but look them up on-line if interested. Again, they would not be my choice for a 12' boat with low HP motor.

Summary - On a small boat like that, with 2 people, I'd keep the 2nd person amidships and out of the bow. See if that helps. Move your fuel tank to the bow if/when running alone, but also test different positions of the OB trim angle pin.

But :shock: heed some CAUTION please ... you do not want that pin in so close to the hull that the force of the motor pushes the bow DOWN into the water. That is called "bow steer" and it is a VERY dangerous condition! It can manifest itself in literally seconds, where at one second you'd be OK and then next second it would forcibly push the bow to the side FAST and throw you out of the boat ... we don't want that to happen to our British compatriots!

FYI, there's a great bunch of knowledgeable people here, so if I erred or missed something - they'll set you straight!


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PostPosted: 13 Jul 2016, 12:49 

Joined: 29 Jun 2016, 10:12
Posts: 21
Thanks dale,
This is a very useful post!


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