Beginners!!

[montego]

Hi all!
Intending to join you all by buying a motor cruiser. I have a budget of about £20,000 to spend & would like to know if anyone can suggest a good secondhand type of boat I could go for that is preferably 30 feet or more as it needs to have good seagoing capabilities in this windy corner of Scotland!!
Also I would prefer the reliability factor of twin diesels.
Any advice on marinas for basing the boat in this area?
Also since we would be costal cruising I feel we should get some training before taking to the high seas, does anyone know what the minimum courses we should complete before taking to the high seas & what their costs are?
Thanks..

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[DavidJ]

Hi and welcome
Regarding the type of boat there is a fundamental decision to be made. A planning boat or a displacement.
Others will describe the characteristics of a displacement boat better than me but they are stable in rough weather and I guess 10knots is about it. They are economical.
Planning boats will zoom at 25-35 knots but anything more than a force 4-5 will become uncomfotable and not much fun. They are seriously uneconomical (50 lires/hr ++) but great great fun.
David


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[Divemaster1]

Welcome to the forum !

Before selecting "the right boat" for you, you need to understand types of hulls and bottom shapes (no jokes please) that are available, and know what they will - or will not - do for you.

On occations I have been accused of "going on a bit", so my apologies in advance of this rather long reply to one simple question (believe you have three).

Displacement hull will always displace (push away) water equal to its total weight. If its total weight is equal to the weight of the water that it's displacing, the boat will float (a great benefit for a boat). 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 that it is creating. At this point, the hull has reached its maximum hull speed. Adding additional horsepower after this point only makes the waves bigger, with very little or no increase in the speed of the boat.
To get a close approximation of what the maximum hull speed of any displacement hull boat will be, you can use this formula:
1.34 X the Square Root of the Boat's Waterline Length (This is Theoretical Maximum Hull Speed)
Example: If your waterline length is 30 ft, multiply 1.34 by the square root of 30 (5.48). 1.34 x 5.48 = 7.3. The product of this multiplication, 7.3, is the boat's maximum hull speed in knots.
Round bottom boats are the basic displacement hull design. Some advantages of a displacement hull are 1. a relatively small engine can easily drive it; thus, its ability to travel long distances is outstanding, and 2. because it's travelling through the water, not on top of it, it has a very smooth, seaworthy ride. However, an obvious disadvantage is that this boat hull is slow. Displacement hulls have a tendency to roll on waves from the side, which may be un-comfortable.

Planning hull is when either not moving or going very slowly, it is, in effect, a displacement hull. As power and speed increase, however, a planning hull lifts itself up on top of its own bow wave. This causes the boat to displace much less water. As a result, there is much less wetted surface on the hull bottom, meaning much less friction as well. The speed of the boat will now increase at a great rate. With this hull, the more horsepower added, the faster the boat will go. The advantage of a planning hull is that it is capable of much greater speed. Just keep adding horsepower and away you go! However, a disadvantage is that the boat is no longer going through the waves, but is now going from one wave top to the next. Consequently, as the waves get larger, the pounding of the boat increases. This, at the least, causes crew discomfort. At its worst, pounding can injure passengers and cause considerable damage to the boat's hull and equipment.

Semi-displacement hull, generally seen on larger cruisers, has some lift capability. This is shown by the fact that as speed increases, the forward part of the hull lifts up and allows the boat to exceed its maximum displacement speed. Some disadvantages to semi-displacement hulled boats are that they need much bigger engines and consume much more fuel for comparable speeds of a planning hull. Normally you would find a semi-displacement hull having good sea keeping abilities, and performing well in displacement mode (slow speed manoeuvring and reduced speed in rough weather). Although “wetter” (more spray over the boat in rough weather), you will find the semi-displacement hull more comfortable in rough weather than a planning hull, and may be a good compromise for you with respect to speed and sea keeping abilities.

There are many other combinations of hull shapes. Some are Vee shaped forward and flat further aft. Others are Vee shaped forward and round further aft and so on. All of these many shapes (compromises) are attempts by the boat manufacturers to make the boat perform the way that the buyer expects it to perform. Again, a it is worth noting that no one boat is going to answer everyone's needs!


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[Divemaster1]

Twin Diesels - reliability

As previous posts in this forum will confirm, there are other issues than just having a "mechanical redundancy" built in with a twin installation.

Obvious there are benefits such as dual propulsion units and mechanical redundancy, but other things you need to consider are:

1) Maintenance cost ... 2x vs 1
2) Accessibility (for maintenance tasks above).. If parts of the engine(s) are not easily accessible, would you do those frequent checks, or would you adopt the thought of "well if one goes down, the other will bring me home". One could argue that people relying on one single engine (including a lot of fishing vessels), are probably keeping their engine in better condition that the ones with twin's
3) Single or dual fuel supply (with or without crossover) for fuel contamination precautions
4) Performance / vs fuel economy (One large single will give better performance and lower fuel costs than two mounting to equal HP)
5) Aquisition cost
6) Propulsion exposure ( Single shaft tend to be protected by skeg) whilst twins normally are exposed as the deepest part of the boat.
7) Replacement cost (as you are looking at a "older vessel" 30 ft + @ £20K , you may have to replace the engines sooner than you think, as the installation is most likely to be more than 15 years old)

Will stop here as I do not wish to drone on too much...

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[qsiv]

Much sense there, but I would take issue with you saying that a planing hull doesnt displace as much water when it's planing as it does in displacement mode.

Providing we ignore aerodynamic lift (which is only material on tunnel hull/catamarans at speeds in excess of about 50kts), then the boat MUST displace it's own weight, otherwise it will sink. The difference is that the lift is generated dynamically due to the angle of incidence of the planing surface moving through the water. Water will still be displaced, but due to the dynamics this will manifest itself as waves.

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[Divemaster1]

Yes, should have stated that the "wetted surface" and as such "friction" is less (resulting in increased speed).... it still has to displace the same volume of water... Thank you for the correction...

<hr width=100% size=1>Alf

 

[Alistairr]

As a fellow scot, what part of Scotland are you in and what area are you wanting to sail in?


Cheers.

<hr width=100% size=1>"INDIANA Has Been Born"
<A target="_blank" HREF=http://www.hamptonandmcmurray.co.uk>Hampton and McMurray</A>

 

[LiamS]

WOW..........I get the impression that montego is looking for a recommended make or model to suit his needs I dont think he is planning on designing and building a craft from scratch.OUCH.....................TOO MUCH INFORMATION.

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[oldgit]

Err umm one insignificant question ....Do you intend trying to sleep on the thing.
for instance if need to sleep on thing for a few days,you will need cabin cruiser(quickish but not much cop in lumpy weather) type boat.Lots of cover etc,but if intend maybe for fishing and days out just a couple of berths and galley will suffice.Perhaps older mitchell or starfish.
Friend recently sold 30ft starfish with 250 hp engine.
10 year old boat and it was for sale at 23k.Sold at 20k.

<hr width=100% size=1>My little Princess/forums/images/icons/laugh.gifthe 33 of course.