What makes a boat suitable for coastal use ?

[Loggo]

Can I ask for a little enlightened input please.

The story so far - My wife and I are looking to expand out boaty horizons and, whilst our present riverboat with her 50 hp Nanni has been excellent on the river (and dipped her hull in the salty stuff on occasion) we would like to have a larger boat with a more powerful engine (s) to enable us to try a little coastal boating.

We have viewed a few boats around our target 34' length with shaft drive, semi-displacement hull and a single engine (Typically 200 hp Volvo or 187 hp Yanmar). Whilst this would provide the economy we would like whilst on the river and we hoped would give around 12-14 knots at sea we are being told that anything less than a pair of 200's will simply not be up to the job.

We read of Displacement hulled Trawler and Dutch steel boats with little more than 80 hp being used at sea regularly - although I guess slowly - and have been wondering if we can get away with a single engine at sea or whether we will be left wishing we had gone for a twin engine set up in the first place.

Any thoughts ?

 

[Jurgen]

Don't know much about displacement boats but re what makes a good sea boat you will get a 100 different answers and there will probably be merit in all of them.

As for engines my thoughts are 2 is better simply for security, if 1 goes pop you can still get home. Cant imagine how I would feel going round Portland bill and having an engine failure, very scared is the answer.

2 engines however does bring additional cost. Am sure many of the owners of single engine craft will be along with some better advice than mine lol.

either way good luck with your search and remember to post pics of your choices.

 

[No Regrets]

Scandinavian boats are pretty good all-rounders!

 

[Chris_d]

The problem with a boat of that size is 12-14knts is very awkward speed to want to cruise at, its past displacement speed of 7-8knts but not over the hump to start planing at 16-18knts. So a lot of power is required to produce the modest speed, SD hulls are happy at this speed but a 34ft hull will need all of that 200hp to achieve it so in practice crising speed will be lower and not very economical. So often it is better to opt for more power and achieve the same mpg at planing speeds of 20-25knts.There are many SD Brooms, Haines, Atlantics in this size range and most are twin engined to achieve good speeds at sea but are still almost as economical on rivers as the single setups.

 

[Loggo]

Scandinavian boats are pretty good all-rounders!

Thanks NR. My feelings exactly - single engine - sea friendly - well thought of.

Unfortunately Mrs. Loggo will not hear of a galley on the same level as the social area. It just has to be downstairs. So rejected with no chance of appeal !

 

[Canopy Locked]

Just to give you an idea . I used to have a Mitchell 31 Mk2 - this is a semi displacement with good sea keeping qualities - the boat had a 320hp Nanni (single engine) fitted. This drove it 14-15 kts cruise. However when I had a new (professionally calculated) prop fitted - I got a cruise of 16 kts for the same RPM or 14 kts but dropping almost 200 rpm

While a twin engine boat brings benefits in security and manoeuvrability, you need to consider the extra costs. IMHO I believe that if a diesel engine is maintained well, and supplied with clean air and clean fuel.. then there's very little worry about. - Invest in a good fuel pre-filter system rather than a 2nd engine.

I would suggest that for a 34ft boat on a single engine that at least 300 hp would be desirable..... but don't forget about the prop.. you'd be amazed at how much you can improve the performance by simply getter a correctly pitched prop for the engine.

 

[oldgit]

Personal take on what makes a good sea boat is the hull.the engines give you speed and the ability to go further during the hours of day light.
A recent for instance.Our club cruises round to the London river every year,either to one of the London marinas(when they can be arsed to book us in) or up above the lock to Teddington .
Right on the dot some crummy low appears on the weather front to impede our progress up Sea Reach,cue lots of crashing around and crockery hitting the floor.
You will hear lots of lots of stories about what wonderful sea boats certain builders produce ,but from my point of view at the back of the fleet,all of them were bouncing around like a bunch of corks at the cruise speed of 12 knots.
The boats on the cruise included several Turbo/Sedan 36,a similar sized Hardy and a big sealine among others ,no doubt the skippers would claim that things for them would improve at higher speeds, but if you are forced to travel slower big engines are not going to make the ride any more comfortable.
My present boat is very comfortable in confused seas and fine for 50/60 mile local trips but its just to slow to go anywhere beyond that..We are looking around for something quicker.

 

[Loggo]

Thanks Oldgit, did you have the twin Perkins 135's or something bigger? That is a good point regarding range in a days cruise - not sure if 60 miles in a day isn't quite enough for me though. I feel the need to moor and dig out the Jameson after all that banging about.

 

[PCUK]

Medway to Thames can hardly be called 'coastal', yes it gets pretty lumpy around there at times but nothing like round the corner the other way. A good sea boat will cruise at 6-7 knots with a small engine or fast and expensively with big engines, the big engine boat will eventually be forced to slow as the weather deteriorates so engine size has nothing to do with the boat's ability. In the end it is the skill of the crew that decides whether the boat is good at sea or not.

 

[Jim@sea]

2 engines however does bring additional cost.

I would rather have an older boat with twin engines than a newer boat with a single engine. and yes it does cost more to service them but service parts are cheap if you can do it yourself.

 

[Surfacesub]

It would be interesting to know why one engine is unreliable? e.g. what in the main actually occurs to an engine in this configuration, to render it powerless.

 

[Wavey]

It would be interesting to know why one engine is unreliable?

It's not. Take a look around our coast at the vast majority of fishing boats whose livelihood depends on engine reliability. Most have singles. The Dutch have built sizeable single engine boats for years without issue. Good maintenance is the key ( and a degree of engineering ability to fix basic issues if they occur).

If you can afford it, and if speed is a box that needs to be ticked, then twins is the way to go. It does give you peace of mind although fuel issues (as I had some years back when delivering a 32ft Coronet) can end up affecting both engines and negates the argument to a degree.

 

[Chris_d]

It would be interesting to know why one engine is unreliable? e.g. what in the main actually occurs to an engine in this configuration, to render it powerless.

Assuming a well maintained engine then it shouldn't matter, worse thing for me is prop fouling. Although the only time this has happened to me in tidal waters a huge rope stopped both engines!

 

[Beamishken]

Don't see why the negativity towards a displacement single engined motorboat for coastal use. There's plenty of yachts go to sea with tiny little engines & never put up a sail unless the winds in the right direction & the suns shining i doubt many sailers could get themselves out of trouble with their sails in a realy tricky situation .

 

[Chris_d]

Don't see why the negativity towards a displacement single engined motorboat for coastal use. There's plenty of yachts go to sea with tiny little engines & never put up a sail unless the winds in the right direction & the suns shining i doubt many sailers could get themselves out of trouble with their sails in a realy tricky situation .

What negativity?

 

[piratos]

Can I ask for a little enlightened input please.

The story so far - My wife and I are looking to expand out boaty horizons and, whilst our present riverboat with her 50 hp Nanni has been excellent on the river (and dipped her hull in the salty stuff on occasion) we would like to have a larger boat with a more powerful engine (s) to enable us to try a little coastal boating.

We have viewed a few boats around our target 34' length with shaft drive, semi-displacement hull and a single engine (Typically 200 hp Volvo or 187 hp Yanmar). Whilst this would provide the economy we would like whilst on the river and we hoped would give around 12-14 knots at sea we are being told that anything less than a pair of 200's will simply not be up to the job.

We read of Displacement hulled Trawler and Dutch steel boats with little more than 80 hp being used at sea regularly - although I guess slowly - and have been wondering if we can get away with a single engine at sea or whether we will be left wishing we had gone for a twin engine set up in the first place.

Any thoughts ?

As others already said, there will be hundreds of opinions on whats required for a good boat for the coast/sea. Fact is that a perfect boat simply doest exist. The mojority of this forum will opt for twin engines, and speed. In other forums they may have different views. Just consider how exposed twin props usually are vs single prop ! What kind of advantage is speed if the port is closed till next highwater ?

Cruising Holland up to the west coast of denmark you will meet several of the dutch steel type boats - all of them are single engine displacement boats and doest fit the major opinion of this forum. Last summer we cruised to Poland and back - and we regularly met the same single engine steel boat (If I remember right a Proficiat 11/1200 from Emden) - so yes they can do it as well.

On the other side there are other important things than speed when cruising. Understand your wife wants cooking only below. Does she want an open cockpit for the evening drink ? does she want a Flybridge ? what about heating ? Tank capacity/range ? easy engine access ? easy access to (fuel) filter etc etc

Not all ships are built like the swedish warship Vasa (she capsized and sank on her maiden voyage) - but there are many bad ships around, and the pro adopt the the ship and not the other way round. Find the boat that fit most of your own requirements, and use it best possible. If it means you have to cruise at 8 knots - so what ? or if you want speeds of 50 knots then buy a rib, and spend the nights in a hotel

 

[Spi D]

Displacement hulls will cruise at a speed according to the waterline length (length in m = knots), so any excess power will be of no use.

The amount of hp needed relates to the diplacement and hull shape. If planing hull a lot more power is needed.

FWIW this is twin 175 hp, ready-togo weight 6-7 tons, planing hull

Top speed up to 24 knots depending on load.

 

[BruceK]

A full displacement hull would give you best fuel economy and better sea keeping as a general rule. A semi displacement at that size and power (34 ft and 200Hp) would be the worst for fuel economy at cruising speeds as it would not get on the plane effectively and squander a lot of power or if it somehow did it would be marginal and likely to be knocked off quite easily, however they are more fuel efficient than displacement hulls at displacement speeds. It will not be as stable as a full displacement at displacement speeds and quite likely rather volatile at cruising speeds especially in a following or quarter seas. A Planing hull for the size you are after gives the best compromise. Fuel efficient at displacement speed, fuel efficient at planing speed (relative) but a big inefficient area in between 8-17knts and but not as stable as the other two.

One engine or two? Well this sums it up best: http://www.passagemaker.com/articles/technical/engines/single-or-twin-engines-which-is-best-2/

If you are after a SD, single engine and Scandinavian, you could do worse than having a look at this: http://www.networkyachtbrokers.co.uk/boats_for_sale/Tresfjord_Nova_31-04268.html/

 

[oldgit]

Thanks Oldgit, did you have the twin Perkins 135's or something bigger? That is a good point regarding range in a days cruise - not sure if 60 miles in a day isn't quite enough for me though. I feel the need to moor and dig out the Jameson after all that banging about.

We have a nice pair of M135 HP engines.
Six cylinders at a litre per piston.Loads of nice low down grunt.
The boat is certainly capable of longer days...but not me.

 

[oldgit]

, yes it gets pretty lumpy around there at times but nothing like round the corner the other way.

Yer.....but round here we have to look at the depth sounder every now and then .