Helm Air

[Robski97]

Tim,
I have one dedicated 4" round vent at the helm . two additional vents blow air on the first mates seat. On a sunny day u dont feel a thing. that why i said what i said . When the suns down its great but as far as feeling the air blowing on u ... nope nada. LARGER vents ... LARGER DUCTS = MORE CFM ...

Rob

 

[Four Suns]

My system has 2 ducts that are about 7x12 inches each and then two smaller ducts at the helm... and it moves a lot of air.

I think Rob brought up a good point in that the additional AC units/BTU size may be dictated by electrical capacity of the boat. The design of the electrical system and components doesn't have a lot of extra capacity on my boat... dumping in a big AC unit may overload the generator, etc... I overloaded the 12v side of my system by doubling the wattage in all the cabin lights and deadened the batteries even with the charger running... so you have to look at the whole system...

 

[douglee25]

Tim,
I have one dedicated 4" round vent at the helm . two additional vents blow air on the first mates seat. On a sunny day u dont feel a thing. that why i said what i said . When the suns down its great but as far as feeling the air blowing on u ... nope nada. LARGER vents ... LARGER DUCTS = MORE CFM ...

Rob

Larger ducts = less air velocity

Technically you should 'feel' more air with smaller ducts.

Doug

Edit: Look up High Velocity AC on google. I'm wondering if looking at the problem from a different angle may present a solution. Possibly going to a smaller vent may help?

 

[Gimme Time]

Anything less than 24,000 BTUs doesn't have a chance in hell of making a dent when you need it and few 10KW or less gen sets will run it along with other loads on the boat.

If you check around most units don't exceed 16-18,000 BTUs on 120 volt power which is what most small gen sets put out. Hence the reason you'll typically find 12-18,000 BTU units on smaller boats.

It's the gen set's power capability vs, the heat gain of the space being conditioned. Don't waste your time or money unless you have or want to provide the power you need to run a bigger system.

 

[timinfla2]

Tim,
I have one dedicated 4" round vent at the helm . two additional vents blow air on the first mates seat. On a sunny day u dont feel a thing. that why i said what i said . When the suns down its great but as far as feeling the air blowing on u ... nope nada. LARGER vents ... LARGER DUCTS = MORE CFM ...

Rob

Ah, good point. So it's not even hardly providing any cool air on you alone, let alone the rest of the cockpit. That's too bad - I'll have to ask my buddy how he gets his to work so well.

Heck, I'm even thinking just a strong fan to provide some air would be a step up on those windless hot days...

 

[fc3]

Well, sort of. I ran through all of the number for a small boat because I was thinking of adding cockpit air. There is not enough power to start a compressor while another is running. You can't have two compressors. So you need to remove the existing unit for an split evaporator in the cabin and one or two evaporator in the cockpit. All work from a single compressor in the engine room. A 2.5 ton remote compressor draws about 8 to 10 amps at full load. Figure 2 to 3 remote blowers for another 3 to 4 amps for a total of 14. That is just a bit too much for a small genset of 4-5Kw. It might work, but compressor start could be a problem since the generator can only provide about 18 - 20 amps. It's pretty easy to rewire a Westerbeke to provide 240 instead of 120, but getting the power (amps) is another issue. Even if the compressor did start and run, there's precious little extra power for anything else.

I almost found someone who had a trashed engine for a 7.2 Kw Westerbeke to sell me the bad unit. It's trivial to substitute my good engine for his bad one, but I never got it. Oh well. It's not worth buying a new genset and the A/C components to make it work, so I'll just wait until the next boat. But if I ever do find someone with a bad Westerbeke engine, I may do it. The cost might almost reach reasonable.

Best regards,
Frank

 

[tadskelton]

I had a 2004 340 Sundancer and had a 18,000 btu cockpit ac/heat unit installed under the helm seat. Worked off of shore power or the generator. It worked pretty well. The cost was a few thousand.