The Salty Bottom Inaugural Rendevous

[Antares_9]

Here's a proper ship Mark, not sure if the accomodation (or indeed the styling ) will suit but worth a look.

Channel islands 32

http://www.boatsandoutboards.co.uk/view/MOR440

[C.Ricko]

Christ David, it has a blue hull.

I hardly think Mark is a professional just yet

[Guest]

I think this explains the semi displacement / planing difference very well although it was written for yacht owners I am sure the same principles still apply to us mere mortals although for aeroplane at the end read car.

Jonathan

Displacement, Planing and Semi-displacement hulls

When buying your first yacht, it is important to know something of the different types of hull design and bottom profiles, and to understand what set of compromises these will offer you.

Hull designs can be broadly categorised into three different types: displacement hulls, semi-displacement hulls, and planing hulls.

The displacement hull displaces water equal to its total weight. As the displacement hull begins to move through the water, small waves appear at the bow and further aft along the hull. When speed is increased, these waves grow larger and the distance between them increases, until the boat is riding between the two waves at the bow and stern. At this point, the hull has reached its maximum hull speed. Adding additional horsepower (or sail power) after this point only makes the waves bigger, with very little or no increase in the speed of the boat.

There is a simple empirical formula to work out the hull speed of a diplacement hull in knots: 1.39 x the Square Root of the Boat's Waterline Length in feet. For example, if your waterline length is 100 ft, multiply 1.39 by the square root of 100 gives a hull speed of 13.4 knots.

Displacement hulls have several advantages, often overlooked by newcomers to the yacht market. They require relatively little horsepower to drive them through the water, so the fuel consumption of the yacht is much lower. Smaller engines cost less to buy and maintain. Because the yacht pushes aside the waves rather than riding over the top, its ride is smooth and seaworthy. Because there is plenty of hull below the waterline, the yacht tends to be stable and comfortable at anchor (where yachts spend most of their time). And finally the lower speed of the yacht means that appendices such as zero-speed stabilisers and azipods can be added to the design.

First time buyers, however, are too often seduced by the top speed of a yacht. If you really must have speed, then you need either a planing hull or a semi-displacement hull.

When a planing hull is either not moving or going very slowly it works like a displacement hull. However, by adding lots of horsepower, a planing hull will rise up over its bow-wave, causing the boat to displace much less water. As a result, there is much less wetted surface on the hull bottom, meaning less friction as well. The speed of the boat will now increase at a great rate. With this hull, the more horsepower you add, the faster the boat will go.

However, this great speed comes with some big downsides. The boat is now skimming over the waves which is great in flat water, but even in a mild chop the pounding and vibration become very severe. At best, this is just uncomfortable for crew and passengers, but worse is that it greatly adds to wear and tear on the yacht. If the yacht slows down and reverts to displacement mode, the flat bottom of a planing hull and short waterline length make for a rolling and pitching ride. The same can be said for the ride at anchor. The flat bottom of a planing hull also means that the yacht suffers greatly from windage, and so can be hard work to berth, even if fitted with bow and stern thrusters. High speed planing yachts are often combined with Arnesen surface drives for yet more speed, which makes the captain's job even harder when manouevring at low speed. And it is nigh on impossible to combine a planing hull with stabilisers because of the drag they cause (though I might write something about gyro stabilisers soon…). Planing hulls are generally used by smaller dayboats, but some fairly large open yachts (Mangusta and the likes) are designed to be fully planing hulls.

The semi-displacement hull is a design that attempts to combine some attributes of displacement hulls with some features of planing hulls. It is generally used in mid-range flybridge cruisers of 50-100 ft in length. The semi-displacement hull never completely planes, but relies on a flat forefoot and lots of horsepower to drive the yacht a little bit over its bow-wave, generating some lift. Effectively, the yacht is always driving uphill on its own bow-wave – so fuel consumption is very high. The yacht can be heavier than a full planing yacht, so it can be a little more stable in a sea or at anchor, but never as seaworthy as a full displacement yacht.

These basic types of hull can all be refined by the designer to seek the compromise that is required, for the perrformance and sea conditions that the yacht is expected to meet. Some hulls may be v-shaped forward and flat further aft, others may be v-shaped forward and round further aft and so on. There are also a few radical designs that step out of the traditional mould completely – eg check out the M-hull.

But the lesson here is before buying any yacht, think carefully about your real requirements and expectations. Try not to fall into the common mistake of an inexperienced buyer of being seduced by the yachts top-speed. All too often we have clients who have learnt the hard way, and come to us with a high-speed lightweight, high-depreciation, high-maintenance open planing yacht that they now want to trade in for a slow, comfortable, cheap to run, displacement yacht. As one wise client said to us recently, “If I want to go somewhere fast, I use my aeroplane. If I use my yacht, it is because I am on holiday and have the time".

[Guest]

Forgot to add Mark have you seen this one for sale at Newark.

http://www.newark-marina.co.uk/index.ph ... ils&id=199

Jonathan

[mbird]

Right, back from Essex (haven't been to Walton for years!). The Sealine 305 was tatty to say the least!

The canopy needs replacing, as does all the upholstery, all the anodes. Inside the fridge were 2 pints of milk and a tub of butter that had probably been there 2-3 months judging by the mould growth inside the fridge . The whole boat stank of fags, as there were still full ash trays everywhere. How anyone expects to sell a boat in that state is beyond me .The engines didn't look too bad, but one of them had a couple of puddles of coolant sitting ontop of the head, and the other had hardly any water in the header tank. The people have only owned it since March this year, and apparently the wife's hatred of boats is forcing the sale.

I think this one would need a lot of work. Do-able as a project at the right price, but the engine side of things worries me a bit.

Now, on the other hand, I've just had an interesting conversation with a chap about this boat http://motorboats.apolloduck.co.uk/feature.phtml?id=105179. Any comments peeps?? It's down in Plymouth so a bloody long drive to go look at it . Him and his wife have used it all through France and the south coast, but it originated from Beccles. Looks quite interesting methinks, if some deal can be done on the price

[Guest chriscraft]

Hi,

on the face of it it looks a great little ship,only reservation is the price!!,look s quiete roomy though i like it!!

[senator]

Looks Ideal for the work you are looking to do Mark, will have a run of keel for the rivers and should have a capable sea hull if a little slow.

You will have to make up beds but there are loads of seperate areas, always handy when the kids want to bring friends.

Looks like it will fit under the bridges but I would ask about its sea handling on YBW.com.

I would be a little suspicious of the fuel consumption, my 8hp outboard on the dinghy uses more than that, maybe it could do it at tickover on the river but surely not at sea

Run a mile from the 305, amazes me how anyone lets a boat get in that state and even more that they would try and sell it like that but unfortunately it is typical of lots of boats on brokerage. if the rest of the boat is in that state you can bet it has not been maintained for a very long time.

Ian

[mbird]

only reservation is the price!!

We have already spoken to the owners on that score and have a better understanding of where they need to be.

[Happy Jax 3]

Looks like a nice boat Mark, added advantage of being a semi displacement on shafts. I like the idea of the aft cabin. I think 8 ltrs per hour per engine or at least at river speeds as Ian said. Shafts are always more economical than out drives though.

It would be a test for your newly learnt navigation skills bringing it back from Plymouth. If you need a crew member for assistance you know where I am.

[senator]

Shafts are always more economical than out drives though.

Think you may find that it is the other way round Colin, out drives are 30% more efficient due to reduced drag and more efficient transfer of power from the gearbox.

Ian

[Guest]

Now we're talking. A friend of mine had one of these and is partly what made me buy Birchwood. The hull has the same underwater profile as crackerjack and the interior is hand built and therefore will come apart by hand if you need to get at things. Engine and proformance sound about right although they dit fit bigger engines in them. eight liters an hour would be displacement speed on two engines, you could halve this at river speed on one engine. Cruising speed 13 kts should be about 20 liters an hour and if you sleep in the back cabin you're garanteed tea in bed.

Jonathan

Ps if you need crew to bring it round the coast at this time of year you know where Colin is.

[Guest]

Mark can I throw this one in at the same money. Might be worth a cheeky offer.

http://www.theyachtmarket.com/boats_for_sale/62613/

Jonathan

[mbird]

Oh nuts, tactical error ....

We have just finished watching "The Perfect Storm". After all my hard work convincing her the sea was a great idea ...

[mbird]

Ps if you need crew to bring it round the coast at this time of year you know where Colin is.

A big lorry sounds a much more sensible idea

[mbird]

Mark can I throw this one in at the same money. Might be worth a cheeky offer.

http://www.theyachtmarket.com/boats_for_sale/62613/

Jonathan

Already tried that one Jonathon, they wouldn't drop below £41k

[Guest]

Already tried that one Jonathon, they wouldn't drop below £41k

41K is a good place to start from. give them time,