New Project Beam Trawler

The workflow of a trawler, as is well known, is very different depending on the time. The boat has to go quickly to where it goes fishing. When fishing they need a lot of power to fixed point. Once the work is over, must return to port as quickly as possible. These are totally contradictory conditions. Although the range of Foud Numbers is constant in all circumstances, no boat forms are best suited to optimize its speed. For example, you need a very fat aft body, little hydrodynamics. What does the owner want, very high speed or pull force ....?
On ships of which I speak, the Cb = 0.19, or less. I know that this value depends on how you take the dimensions involved in it, but will always be a low value.

 

Cb 0.019? Quite a low value. Something like this?

 

Maybe 0.19 is worth a little low. Let's say 0.20 or 0.22.
See photo of the boat I'm talking about. You may find it a little strange but, in the Spanish Mediterranean coast is very normal this type and size of boat.

 

Ah Ok. Looks like a lobster boat type hull. Ours is like I pictured and commonly uses marinized auto truck engines with automotive transmissions. They switch gears while trawling.

I don't have the data yet how long and how slow when they trawl. I am just riding on the idea you said you installed bulbous bow on some and the master was happy. So I said, why not?

Maybe some fishing boats will fit within the band. Handline fishing boats travel to the fishing ground and stop to fish. It carries a lot of crushed ice going out so it is fully loaded.There are also big purse seiners that goes to the fishing grounds, stop and lower the small boats that will tow and encircle the fish with nets.

I am just contemplating on the idea. If the numbers fits, there might be a room for improvement.

 

We agree. Always investigate. Besides what theoretical studies can say, besides testing tank experiences, if possible make them, the most important is the satisfaction of the owner who is the only one who knows how he'll handle his boat.

 

So I have a problem because I need a 585 ton displacement but with a block coefficient 0,19 , the length and beam will have to increase more than 30 meters and 7,8 meters to get a right draft

 

Question

Where you find that Cb 0.19 ?

 

I have seen a wide block coefficient range in this ships, just I thought this coefficient was 0,69 before reading the replies, now I don't know very well.

0,19-0,22 seems quite low, but Are you including the keel in the calculus? Then it Could be ok..

 

Of course not. You have several choices for semi displacement hull forms (attached). TANSIL's example is typical of Maine's lobster type hull, light displacement, overdriven, typical of fishing boats. There was a study of different variations of this type which was featured in PB magazine some years back. Sorry, I lost my copy, cannot post it.

I have adopted and made several designs of the NPL type hull for handline fishing boat (up to 50 tons disp.) and was succesfull. This type of hull, also called lobster boat hull was covered by PB magazine. (i will look for the issue). If you want to play around with NPL hull, Leo's Michlet has this as an example hull type.

These semi displacement hull has Cb from 0.4 to 0.58. Any higher and Series 60 lines (Cb 0.60 to 0.80) can also be considered depending on your SOR.

 

If in the ship's of post # 33 we discount the keel, the values ​​for the depth of 2.2 m correspond to a depth of 3.5 m. In this draft the Cb approaches the value 0.4. Therefore, although one can not generalize because fishing vessels do not correspond to a standard type, it seems that everyone is talking about similar Cb.
These boats, as pointed by rxcomposite, are between 50 and 65 tons. Therefore, with a displacement of 585 tons, you should go to a type of boat totally different.

 

SixM,

I did some preliminary design to gain an insight into your initial requirements of 585 tons.

Below are the results. You should investigate hull forms in the 0.50+ Cb. Maybe even a series 60 hull with bulbous in the range of 0.60 Cb.

I like NPL hull (similar to TANSL post) because of the sharp entry, less bottom slamming. Unfortunately, the resistance analysis data I have is only for 0.40 Cb which is typical for the said type of hull.

Note that the image I posted is a preliminary design study, not an all out design. Many things have to be considered, but the graphs and tables included should guide you.

 

It is really nice! thank you, so following your study my ship with 585 tons disp might have a 42 m length (now 30 m), and my froude number is around 0,38 then my block coefficient is around 0,56 (now 0,69), right? It seem a good choice.

But I have a doubt about Marin info because I have an article about Emanuelle trawler from there and it have 990 tons disp with only 35 m Lwl.

 

SixM,

42m is only a median. I can further reduce the length and increase the Cb if it fits the Watson and Gilfillan line. There are still many combinations to explore like Fn from 0.30 to 0.38.

There is something that is not clear in your SOR. You said shrimp and octupus has a density of 0.50 ton/m3. These specs are for blast frozen processing, not for shrimps preserved in brine and crushed ice which has a density between 1.10 to 1.20 ton/m3. Do you have processing in your boat? Is it is a fish production boat? how many crews do you have?

Is your boat a trawl, dragging nets to catch shrimp and octupus or just a refrigerated cargo carrying blast frozen processed fish to its destination?

 

It is a beam trawl with twins dragging nets and have a processing machine on board to put it in boxes in the refrigerated cellar. But the boxes wheight is added to the specification too.

And crew is around 8 people.

 

?

On post #20 you calculate/declare 18 people. Isn't it correct ?