Poleson Marine diving vessel

Having researched (with the help of a lot of you on here) and discarded a lot of ideas like RIB's, Stabicraft-style vessels etc. I am pretty much set on a 12 x 5.5 metre Poleson Marine hull design to be built from aluminium and then used as a diving vessel to support maritime archaeology here in the Red Sea in Egypt.

The Poleson Marine designs give us tons of deck space which is critical for diving vessels. Part of the reason for this is that the design puts the cabin so far forward which leaves a massive aft deck.

12 metres is the maximum length as anything bigger than that becomes far more complicated to get licenced here locally.

The minimum crewing will be two persons (200 kg), the maximum loading will be 1900 kg (2 crew + 10 divers and their dive gear).

The ideal cruising speed is 24 knots, no particular figure has been determined for needed maximum speed.

Because the local area has seen more than its far share of shipwrecks due to the treacherous reefs including one of the world's worst maritime tragedies we will be making the vessel available to local authorities whenever it is not being used for diving - e.g. night times.

Local sea conditions vary from bathtub smooth to very stacked up and confused 6 foot waves and swells.

Range will need to be 600 nautical miles.

Main questions left now are -

• displacement or planing hull?
• propulsion - the local limit for outboards is 300 hp per engine, no limit for inboards
• waterjets would be nice but are sounding like they might be very expensive
• dynamic positioning would be nice but again the equipment needed for that is sounding very expensive

That is about where it is all at now

 

The cockpit should be positioned as far forward as possible, all right, but that's hardly a reason to go for a particular design. Any design can be fitted with a cabin in the bow. More importante would be to know the size you need for that cabin.
If you want to collect the archaeological finds that can be found in the Red Sea, you should think about placing a crane, of the necessary power, on board.
24 knots as a cruising speed is a high figure. A displacement hull may not be the right one.
Two engines of around 300 hp have a consumption of, say, 35 litres/hour (could be much bigger). The 600 miles of autonomy, at 24 knots cruising speed, suppose 25 hours of operation (25 h x 35 l/h=875 litres). Which leads to the need to have fairly large fuel tanks.
Better than the price of motors or any other equipment, you should check the capacity that there may be in your area to repair or maintain this equipment. A very cheap engine can be too expensive.
6 foot waves and swells is not that tremendous.
You assume 100 kg per crew member and 170 kg per diver. Is that really correct? Have you thought about the weight per square meter that this implies? Consider a very sturdy deck.
I think, and excuse me for saying so, that you should mature the SOR of the boat a lot more.

 

600nm is quite a lot of range which you had not alluded to earlier

not that it is not doable, but 600/20 is 30 hours one way which means sleeping quarters, etc.

if you don't typically need that; probably jerry cans would work

just a few random thoughts

 

Still re that 600 mile range - how did you arrive at this?
Is the nearest fueling station a long distance away from the regular / permanent berth for the vessel?

Re the size of this cabin, will it be a requirement that all of your divers have to be able to be seated comfortably in the wheelhouse while underway?

And re the minimum area of deck space required behind the wheelhouse, how have you calculated / estimated this?
You might find that the wheelhouse on a 12 metre long vessel does not necessarily HAVE to be perched right on the bow, as per the typical Poleson vessels.
It is always an advantage if you can keep weight out of the bow, and especially so with cats.
Hence why the Polesons have these bulbous bows - but they will add to the cost of building, and they might well have some additional resistance, compared to a vessel without them.
The Poleson fishing cats are probably built to a rule where they have to be under a certain length, hence they want to get the most amount of boat into this length.

 

Agree that any design could be fitted with a cabin in the bow - but would it then need to be redesigned to cope with the shift forward of the longitudinal centre of gravity and it would probably need big forefeet like the Poleson to stop it diving over waves? So going with the Poleson design that is already designed to take the cabin at the front makes sense to me. I would like the cabin to be the full width so as we have plenty of room for large screen electronics, desks, etc etc. where everything can be kept dry and locked up.

Collecting anything would require about 12 months of paperwork and meetings and approvals, and most things we would expect to find wouldn't be big enough to require a crane.

Quite possibly - I am open to advice in that. I would also like info on whether displacement or planing hulls handle confused seas in the 4-6 feet range better?

Indeed, but I think that Tommy already puts large tanks on his vessels anyway.

Yanmar's seem quite popular here, also big MAN's, and CAT's, and there is a complete assortment of others as well. There is also one that is painted green that is becoming very popular lately - starts with D - Doosan? possibly.

Not that horrendous, but the confused seas here with 6 foot waves coming from the NW and 6 foot swells coming from the East make for some really mixed up seas. The intervals between them tend to only be 3-4 seconds which adds to the soupy mix.

I would have thought that a commercial vessel's deck would handle 500 kg per square metre?

In which areas?

 

That is mainly for delivery from the shipyard through the Suez Canal down to where the vessel will be based, and then once in operation to prevent the need for the vessel to have to hit the fuelling dock every day as there is usually a queue there. There will be places along the delivery route where the vessel can be tied up to a jetty for the night and the crew spend the night in a hotel, but not all jetties have refuelling facilities - mainly because some of them date back to King Solomon's time - quite literally.

 

It is partly to facilitate delivery from the shipyard through the Suez Canal and then down to where it will be home-ported.

It is not a long way, but fuelling is a painful process as the fuelling "facility" is simply a jetty that has the strength for a road tanker to drive onto - basically each vessel orders a road tanker with how much diesel that want to take onboard, sometimes two captains might be able to coordinate fuel from one tanker but usually things aren't that coordinated here!

No not at all, the divers here normally sit on the bench seats that have their dive gear setup behind them.

Played around with some trial layouts of the deck in CAD, am still moving a few things around.

To us the advantages of having the big aft deck will outweigh the disadvantages you mention unless the disadvantages become too extreme. If the bulbous bows add 5% to the overall construction costs but gain us the big open aft deck then I think that we can live with that, likewise with additional resistance meaning slightly bigger engines needed or more fuel burn then I think that we will live with that too - we are fortunate that diesel is currently US$1.15 per gallon here.

We are operating under a similar rule with a limit of 12 metres and so we want to get the most amount of boat into this length too

 

Do not doubt it, with these waves and, consequently, the reduced speed and waves every 3-4 seconds, a planning boat will be unmanageable.
Bow bulbs on a planing boat does not seem like a logical configuration.
The weight of all the fuel that you will need will be much greater than that of the cabin, no matter how big it is. You will also need other types of tanks, probably large ones. Do not subordinate the shapes of your boat to the position of the cabin, study the weights as a whole. For that, among other things, you must make a much more detailed SOR: you must define everything that will go on the ship, where to place each piece of equipment, with its weights and CoG, materials to use in each element, etc. .

 

After the SOR comes the Design Spiral.

 

The what?

 

The refinement of the SOR. What works and doesn't work. Used to be a hot topic in BD Forum. Is the ship design spiral holding you back? - Simcenter https://blogs.sw.siemens.com/simcenter/ship-design-spiral-simcenter/

 

OK so that helps as it answers one of the questions in my opening post - it sounds like it will need to be a displacement boat. In a way that then answers the next question too as I just can't see a pair of 300 hp outboards pushing a 12 metre displacement hull cat to cruise at 24 knots so the likely answer is going to be inboard diesels - I don't want to go down the Indonesian route of hanging a heap of outboards off the stern. Waterjets have pretty much ruled themselves out as well due to excessive cost vs benefit.

I will to the extent that I have time, but I don't want to reinvent the wheel either if I don't have to and if the Poleson design will do the job quite well - I don't want to try to chase the perfect design instead of quickly settling on something that is good and meets the needs.

 

Specify your mission range. That is from the jetty where you can take in fuel to the diving site and back so that the fuel on board and pax accommodation can be calculated accurately.

600 NM is not a mission range and does not reflect on how the boat is going to be operated normally.

 

Based on the engine configurations I've seen; and the video of the boat underway as well as the pictures of the hull, these are not really planing hulls. 450hp and a top speed of 20kts is not really a planing hull design by speed/hp/length alone..

You are getting a lot of noise now from all of us. And you need to talk directly with the designer.

Questions

1. Are these displacement or planing hulls or somewhere in between?
2. Max hp and top speed at max
3. Range at max hp at cruise, not max speed
4. Max sea state (I expect 100-110% of beam)
5. Typ cruise speed (14kts was nice on the vid)

 

wont that result in maxxing out the pounding of crew in cockpit in a fairly small and fast ocean going boat? I'm thinking it would be A-OK to have SCUBA Ops deck get pounding at speed, because you only have people donning/doffing their SCUBA suits once you are on location and stopped or trolling speed.