New Sportfish CAT Design

[NeumannKG]

I'm currently in the middle of designing a 43' sportfish catamaran and am planning to equip it with an enclosed, air-conditioned pilothouse. Because of the A/C load, I'm considering adding a small diesel genset to power the HVAC system.

This will be my first time incorporating this type of configuration into one of my designs, so I'd love to hear from anyone with experience. I'm interested in recommendations on genset sizing, A/C capacity, installation considerations, noise and vibration isolation, fuel consumption, maintenance access, or any lessons learned that you wish you'd known beforehand.

Any suggestions, best practices, or pitfalls to avoid would be greatly appreciated. Thanks in advance!

 

[bajansailor]

Welcome to the Forum NewmannKG.

Re gen set sizing and A/C capacity, wouldn't this be dependent on how big the deck house is?

I presume that your cat will have petrol outboard engines - or will they be diesel, or inboard engines?

This 45' Grady White has outboard engines, and a 12 KW diesel generator - they mention that she has a 12,000 BTU air con system for the cabin and I think that this has vents in way of the open helm console as well.

https://www.gradywhite.com/models/canyon-456/

Owners will have to be careful that they do not confuse the fillers for the water, diesel and petrol.

 

[NeumannKG]

Welcome to the Forum NewmannKG.

Re gen set sizing and A/C capacity, wouldn't this be dependent on how big the deck house is?

I presume that your cat will have petrol outboard engines - or will they be diesel, or inboard engines?

This 45' Grady White has outboard engines, and a 12 KW diesel generator - they mention that she has a 12,000 BTU air con system for the cabin and I think that this has vents in way of the open helm console as well.

https://www.gradywhite.com/models/canyon-456/

Owners will have to be careful that they do not confuse the fillers for the water, diesel and petrol.

Thank you.

Correct.. The pilot house will be around 200sqft. The I am thinking 8k BTU because aluminum hose and windows all around. So, the electrical load plus hotel load i think i can get away with a 6kw. I was thinking about dometic style AC but someone suggested a split but i only have experience with air cooled split. No one wants to have condenser on the deck of a 1.2mil boat. I was thinking water cooled but don't have experience with that design or operation. Additionally, you are correct the Mains are regular fuel and the genset would be diesel.

 

[bajansailor]

I am sure that other folk who know a lot more than I do about this subject will stop by this thread soon, and I hope that they will also offer opinions.

In the meantime can you tell us a bit more about the design of your new power cat please?
It sounds like an interesting project.

 

[brian eiland]

I am sure that other folk who know a lot more than I do about this subject will stop by this thread soon, and I hope that they will also offer opinions.

In the meantime can you tell us a bit more about the design of your new power cat please?
It sounds like an interesting project.

i'd be interested to here of this also,...as i've done a bigger design, and can reference few smaller ones built on existing hulls.

 

[brian eiland]

i think you might be foolish to try and ac the flybridge,....so much time in and out, in and out.

 

[Rumars]

Since you're designing the boat from scratch you can do what you want, including a gasoline fueled generator to avoid the dual fuel issue. It's a question of designing an enclosure for it that isn't liable to gasoline fumes accumulation, wich is actually possible on a cat.

Generator size is AC surge load (starting) plus hotel loads. For fuel efficiency the inverter generator is better. Constant rpm models work fine if sized for a known load but you have to be careful not run them on a very low load all the time. Better to fit some lithium and a smart inverter to stem the surge loads.
For best sound insulation you want an all watercooled unit, that is watercooling not only the IC engine but also the electric generator head. A dual circuit cooler with wet exhaust is mandatory for me.

Now, if you only use the AC when under power from the main engines or in the marina on shore power, and since the engines are going to be sizable anyway, you can look into the option of fitting additional high power alternators to the propulsion engines. This may or may not be possible with your chosen engines, you have to ask the manufacturer.

I can't comment on A/C selection, but if I paid 1.2 million on a boat and see anything even remotely resembling a Walmart window unit on it I would draw and quarter the designer/builder.
Same if they don't properly insulate the walls and at least attempt to use double glazing (it's not always possible).
My first selection criteria would be the service network the brand has in the operating area, and it's reputation. Sooner or later something has to be done to it regardless of the brand, so I want it mounted relatively accessible for service and someone competent near me.

I know Webasto has a unit designed to be bolted to a main engine (like a car A/C), it could be paired with a small marinized engine or generator, bypassing the electric step and having the entire unit in one spot.

 

[NeumannKG]

i think you might be foolish to try and ac the flybridge,....so much time in and out, in and out.

Yeah, rtehe

i think you might be foolish to try and ac the flybridge,....so much time in and out, in and out.

Yeah, thats definitely a concern but the builder wants it and he had two other vessel previously. We are looking to go more luxury on this one where his older ones are very industrial.

 

[NeumannKG]

Since you're designing the boat from scratch you can do what you want, including a gasoline fueled generator to avoid the dual fuel issue. It's a question of designing an enclosure for it that isn't liable to gasoline fumes accumulation, wich is actually possible on a cat.

Generator size is AC surge load (starting) plus hotel loads. For fuel efficiency the inverter generator is better. Constant rpm models work fine if sized for a known load but you have to be careful not run them on a very low load all the time. Better to fit some lithium and a smart inverter to stem the surge loads.
For best sound insulation you want an all watercooled unit, that is watercooling not only the IC engine but also the electric generator head. A dual circuit cooler with wet exhaust is mandatory for me.

Now, if you only use the AC when under power from the main engines or in the marina on shore power, and since the engines are going to be sizable anyway, you can look into the option of fitting additional high power alternators to the propulsion engines. This may or may not be possible with your chosen engines, you have to ask the manufacturer.

I can't comment on A/C selection, but if I paid 1.2 million on a boat and see anything even remotely resembling a Walmart window unit on it I would draw and quarter the designer/builder.
Same if they don't properly insulate the walls and at least attempt to use double glazing (it's not always possible).
My first selection criteria would be the service network the brand has in the operating area, and it's reputation. Sooner or later something has to be done to it regardless of the brand, so I want it mounted relatively accessible for service and someone competent near me.

I know Webasto has a unit designed to be bolted to a main engine (like a car A/C), it could be paired with a small marinized engine or generator, bypassing the electric step and having the entire unit in one spot.

I was debating diesel or gas but the builder mentioned diesel so it sparked thoughts. I like the inverter idea mainly from noise standpoint. I want thinking about a dometic style or or a watercooled split. No walmart style window units here, lol.

 

[Rumars]

If you can arrange it the nicest option would be to have a dedicated technical space that houses pumps, generator, a/c unit, etc., all mounted on silent blocks. Then you sound insulate the entire room including the door/hatch with heavy mats and foam, and duct the air intake to somewhere people don't usually lounge.

 

[brian eiland]

I never got a return message from this fellow,...nor a translation of the language,...BUT there are some photos

RunningTideYachts.com