NEW. Росомаха (img) русский конкурент Harbercraf / Jetcraft
Byuer Guide Руководство покупателя
Фотографии с выставки "MIBS 2009"
Закон и катер. Постановка на учёт катера со стационарным двигателем.
дюймы в сантиметры
Форумы на тему... с переводом.
Harbercraft
1875 J-Max White Water (img)
2075 White Water
(img)
1875 J-Max XS (img)
2175 XS Фотографии с выставки "Охота и рыбалка - 2008"
Marathon Marine and Northwest Jet Boats (link)
PHANTOM Jet Boats (link)
RiverPro®. (link)
North Silver PRO 675Jet lnk
Росомаха (img)
Tom 525. Томь 525.
Коллекция ссылок на тему: водомёты для судов (Links).
Курс доллара
Друзъя
Stability at Speed: Porpoising versus bow down Стабильность скорости Дельфинирование.
The more power you put to it, the more the boat should lift out of the water and remain
stable. Does yours? A well designed boat will run nose up and stable, through all speed
ranges. Often however, two different things can happen – porpoising or the bow is way
down with the spray line far forward on the boat.
Porpoising is where the nose lifts and falls as the boat runs through the water. This can be
Дельфинирование – это когда нос поднимается и падает, во время движения катера.
quite pronounced and violent at higher speeds. Essentially this happens when there is too
much lift on the bow. As speed builds up, the water pressure on the hull causes the boat
to rise out of the water and into the air. This is exactly what you want the boat to do. On a
well designed boat, this will happen smoothly and the boat will be steady in a fore/aft
motion. Essentially the lifting water pressure on the hull equals the drag/gravity
downward pressure of the boat at all points along the hull. However if the trim on the
boat or the hull design is such that it generates a disproportionate amount of lift on the
bow, the bow will rise out of the water to the point that the lifting forces from the water
pressure can no longer support the bow. Then the bow falls into the water. However it
overcompensates and falls too low into the water and then is driven back up again by the
water pressure on the hull. And thus the cycle (porpoising) continues.
This is the same thing that happens in a prop boat when the motor is trimmed out too far.
Any time you see a boat with the bow (bouncing) up and down it is porpoising. In a prop
………………………………………..прыгнуть/подпрыгивать
boat, when trying to maximize speed you will intentionally (trim) the engine out to lift the
………………………………………………………………(дифферент(овать)
bow and reduce the wetted surface of the hull. However there (reaches) a point when the
…………………………………………………………………(достигать)
porpoising becomes quite (violent) and can (literally) injure someone in the bow. The
………………………… (яростно) (буквально)
difference between prop and jet boat, as discussed later, is that there is no trim (unless
you buy trim tabs) on a jet boat.
Therefore the hull design is critical. This is discussed later in the trim section. That
section also discusses how to fix the problem.
The opposite of the porpoise is the hook or where the boat bow is driven down and the
boat accelerates. As a result the boat tends to (plow) through the water with the spray line
……………………………………………….(пахать/рассекать)
well forward on the boat – sometimes up at or forward of the driver.
At the start of the discussion we stated our (bias). We have a very strong bias (with respect
…………………………………………..(предубеждениея/пристрастия)…(по отношению)
to) the hook. Whereas pretty everyone will agree that porpoising is bad, not everyone
agrees the hook is bad. In fact, many manufacturers intentionally build hooks in. So first
we will describe what it is, and then we will guess why some manufacturers intentionally
build in hooks.
Hooking is done by making the stern portion of the bottom slightly concave. Everything
is fine at slow speed and in fact a hook can actually assist the boat in getting out of the
hole and getting the boat up on plane. This occurs as the stern portion of the concave
forces the water down and therefore creates upward pressure on the bottom and therefore
lift as shown below. The reason it can create faster hole shot, is that typically the heaviest
part of the boat is where the engine is – at the stern. So the more lift at the stern, the faster
the boat gets on plane.
As most sport boats are built for fishing and skiing, many manufacturers intentionally put
a hook in the boat to assist the hole shot. This way the boat can use a smaller motor to get
the boat up on plane.
The second reason is it (prevents porpoising). The hook prevents porpoising as described
………………………(мешать дельфинировать)
below.
As always, however, there is no free lunch. What you gain at one end, you lose at the
other. As the hooked boat begins to accelerate the hook begins to force the stern of the
boat up and the bow down. The faster you go the more the bow goes down. This limits
top end speed and handling. You can see this effect by watching the spray line (the point
where the spray stops coming off the boat which is also where the side exits the water)
move forward on the boat.
Hence the second reason for putting the hook in – to prevent porpoising. As described
above, when the boat is hooked, the faster you go, the more the bow is driven down – it
never gets a chance to lift. Therefore it cannot porpoise. From a manufacturer’s
perspective, this is great. No customer complaints about porpoising boats.
Now back to the hook. You can see the effect of the hook very readily in a boat with trim
tabs or an outboard. Adjust (trim) the tabs or motor downwards while cruising to push the
bow is down. Now adjust your trim so the bow begins to rise. By lifting the bow you will
pick up speed. Also notice that the spray line moves towards to the stern. At a certain
point, it will also feel like a brake has been released. The boat will suddenly handle
easier, feel lighter and more maneuverable and it will ‘dance’.
So now comes the bias part. Although hooks are bad in all boats, it is particularly the case
in jetboats. In our opinion, the most (dreaded) of all jet boating phenomenon is the hook.
……………………………………..(страхи)
We like a boat that performs. Part of that performance means matching your power to the
boat. If you need to hook your boat (to get) the thing on plane, (then either) you have hull
…………………………………(достигнуть/получить)……..(одно из двух)
design issue or not enough power. Our suggestion would be to buy a smaller boat that can
plane on the power you can (afford) or buy a bigger powerplant/engine.
…………………………….(позволить себе)
This (raises) a last reason manufacturers may put hooks in - it limits top end speed. The
…….(подъём)
hook acts as a natural brake – the more power you put to the hull, the more it bow (steers)
……………………………………………………… (бычиться/упираться/зарываться)
– and you also get tired of paying the gas bills associated with the hull drag.
So what is the advantage of getting rid of the hook? You get a boat that continues to rise
smoothly as you apply power. A well tuned boat will have the spray line continually
moving to the stern as speed increases. This results in a boat that requires less water to
run in (a good thing in shallow water), less hull drag and better fuel (mileage). As well you
………………………………………………………………………(выгода/экономия)
get a boat that is more responsive and turns easily. If it is tuned right, it feels like it
‘dances’ when you turn it.
If your boat is hooked you may have an easy or difficult fix. The easy, lucky fix is by
either adjusting the tabs at the end of the hull, if they exist (they are on all Marathon jet
boats) or the jet drive ride plate, if there is one such as on the Mercury jet. Lastly you can
change the angle of the jet nozzle on non-Mercury drives.
If you have a delta type keel and the bow is driven down while accelerating, you will
have a bigger problem. Marathon does not build a delta keel, so we cannot recommend a
fix for this problem.
If these adjustments do not work, you may require major changes to the hull. Before
doing so, make sure you know what you are doing or take it to someone with a known
reputation for such fixes - the fix is as much an art as a science.
In evaluating a boat, look at where the water is coming off the boat at speed? Is it in the
middle or near the transom? Is it a clean line or jagged? Does it move backward as you
accelerate or does it move forward?
As we discussed earlier, generally speaking, the farther back the spray line, the more
efficient the hull, and therefore the faster and more fuel efficient it will be. If it is coming
off at the windshield with a light load, then you have a problem. The spray coming off
the sides of the boat should be relatively ‘clean’ with little turbulence. Turbulance means
drag which means decreased performance and fuel economy.
A lot of little things in the boat add up to big differences on the water.
Boats: What to Look For. НА ЧТО ОБРАТИТЬ ВНИМАНИЕ при покупке лодки.
Введение
Сварные лодки в общем
Наши предпочтения
Buying a Welded Boat for the First Time
Bottom Width and Engine Size and Type.
Stability at Speed: Porpoising versus bow down Стабильность скорости Дельфинирование.
Boat Materials: Aluminum versus Fiberglass . Материалы для катера
Cost differences between glass and aluminum . Сравнение стоимости стекловолокна и алюминия.
Types of Aluminum. Типы алюминия.
Material Thickness
A Word about Welding
Suck marks, caterpillar tracks
Folded, ‘Origami’ Construction
Deadrise (Vee)
Planing Hull Bottom Types Корпус с дном плоского типа
Constant deadrise V (including modified V hulls)
Flat bottom hulls (8 degrees deadrise or less)
Bow Entry Types. Тип носа катера
Radius Bottom Круглое дно.
Lateral Stability During Planing Turns
Bottom Shape and Jet Intake
Planing Ability
Reverse Chines
Bottom Width: Flair is not everything
No Trim.
Hull Construction Standards
Shallow Water Operation
No Exposed Drive
Safety
Thrust line and Center of Gravity In line
Propeller Torque is Different than Impeller Torque
Propulsion Resistance.
Power Plants
Силовая установка.
Derived from Impeller Curves.
RPM Curve Derivation
Conclusion
Hull Resistance.
Boat attitude..
Jet Drives
How jets work .
Impeller
Cut.
Cut, Speed and Load
Wear ring.
Nozzle
Stator.
Hard Anodized.
Cavitation .
Intake
Seals
Mixed flow
Axial flow.
Outboard jet:
Inboard jets:
So, what is the best jet?
Corrosion.....
UHMW...
Jet Diagnosis...
Rattle at Idle (V8 boats)
Speed too low for a Given RPM.
Poor acceleration or ‘holeshot’, combined with high top end
Definitions.
Porpoising .
Chine walk: 9
Ram effect .
Static thrust:
