How many HEADS does a boat really need?

[cyan]

A psuedo-scientific study...
How many heads do we really need to safely avoid a crew emergency?
Conversely, how many do you need for crew happiness?

This is a question that crossed my mind back in the days when my family all shared one bathroom in our little house.
I always suspected that having TWO bathrooms with a bunch of people was not TWICE as good, but EXPONENTIALLY better.
Three or more must just give diminishing returns.
("Better" in the sense of fewer emergencies where someone is pounding on the bathroom door in need.)

Now this question has come up regarding our cruising boat and estimated guest count.
I think the average cruising crew count is often close to 2, but we plan on 4+ for longer passages.
Peggy Hall probably already has the answers, but here is a bit of math to explore this question in depth.

The following analysis makes several assumptions and generalizations.
It does NOT consider male/female differences, and assumes nobody does their business top-side. (our boat doesn't perfectly comply here)
An "emergency" means someone has to go, but all heads are occupied.
Also, it assumes worst-case: everyone is awake during the same 16 hours. (must be anchored!)

Nmins_in_day = waking hours (16) * 60 min/hr = 960 minutes in a waking day
Ncrew = crew count
Nheads = head count
Ppee = probability of a person using head = (16 min per day / 960 waking minutes) = 0.017
Nemergency = minutes per day of emergency head-door-pounding
(note: 16 min per day in the head is taken from a British study of bathroom habits)

Nemergency = [(Ppee)(Ncrew)*(Ppee)(Ncrew-1)*(Ppee)(Ncrew-2)...(Ppee)(Ncrew-Nheads)]*Nmins_in_day

Here is a table of results for a crew count of 2-10 and a heads count of 1-4...

Nemergency (emergency minutes per day)
____________heads_________
______1_____2____3_____4__
crew
2____0.53__0.00__0.00__0.00
3____1.60__0.03__0.00__0.00
4____3.20__0.11__0.00__0.00
5____5.33__0.27__0.01__0.00
6____8.00__0.53__0.03__0.00
7___11.20__0.93__0.06__0.00
8___14.93__1.49__0.12__0.01
9___19.20__2.24__0.22__0.02
10__24.00__3.20__0.37__0.04

Conclusions...
Yes, having 2 heads IS better than twice as good as having 1 head. With 4 crew, 2 vs 1 head is 29 times better!!
TWENTY NINE times the peace.
TWENTY NINE times the happiness.
However adding a 3rd head looks irrelevant until 8 or more crew is on board.
Interestingly, 10 crew with 2 heads will involve 3.2 minutes of door-pounding per day.

A further happiness study could include the opposing forces such as cleaning,maintenance where FEWER heads would be better.
A fancy equation might not be needed to find the perfect number though.
2 heads looks like the ideal count for 3 to 7 crew according to the chart.
Thoughts?

-Cy

[S/V Illusion]

You are kidding, right?

[a64pilot]

Two, only cause you need a back up for any critical piece of equipment.
Although to access our second one would require removal of the washing machine sitting on top of it.

[cyan]

Originally Posted by a64pilot

Two, only cause you need a back up for any critical piece of equipment.
Although to access our second one would require removal of the washing machine sitting on top of it.

That seems like the correct answer, same as the one with the fancy math!

[estarzinger]

hmmm . . . . you carry head spare parts? Right? And you can turn a screwdriver - right? and you do routine annual maintenance - right? And you have a bucket - right? Then you only need one. We sailed twice RTW with one - never an issue. I personally would argue on a boat under about 50' that two is a waste of valuable space.

[JPA Cate]

IME, 6 people can get on all right with one head.

I disagree that it is a mission critical bit of gear, although important, for sure. One can use a bucket if one cannot fix the head. That said, though, there were a lot of plastic toilets glued together with underwater epoxy the year we crossed the pond.

Ann

[Mike OReilly]

My experience growing up with a family of five was that one bathroom was just fine. There were no bathroom emergencies that I recall.

On a smallish cruising boat with crew in the two to four range, I really can't conceive of any reasonable scenarios that would necessitate having two heads. Convenient, sure. But certainly not necessary.

The reason heads are proliferating on cruising boats is b/c bathrooms have already done the same on land. Nothing particularly wrong (or right) about this. Just changing attitudes and affluence.

[Calif.Ted]

"Anyone with more than one head on a sailboat is just asking for trouble." Ted

[hpeer]

TWO. One port, one starboard. Unless you are on a car, the. Then answer is 78.

[Tillsbury]

I agree with two, partly so that one is backup and you don’t need to be dismantling one at sea, and partly so that the owners one is kept clean

The boat I have now has three, plus a shower room. Completely ridiculous. I’m planning to convert one to a Pullman cabin, and one to a laundry/workshop, leaving two each with integral shower.

[atoll]

none,a bucket works just fine..........no moving parts either to break

[a64pilot]

I’m thinking that She who must be obeyed, won’t be pleased with a bucket. Besides the Boat came with it, why remove it?

Number of bedrooms and bathrooms is a status symbol. If you ask someone how big is their house, they will reply four bedrooms, four and a half bathrooms, they don’t tell you in sq Ft.

[StuM]

Originally Posted by Mike OReilly

The reason heads are proliferating on cruising boats is b/c bathrooms have already done the same on land. Nothing particularly wrong (or right) about this. Just changing attitudes and affluence.

I think it has a lot to do with more boats being built for the charter trade. If two or more couples get together to share a charter, frequently they will each want their own facilities.

[cyan]

Originally Posted by StuM

I think it has a lot to do with more boats being built for the charter trade. If two or more couples get together to share a charter, frequently they will each want their own facilities.

This is a really good point. When looking at post-charter used boats, we always felt like there was at least 1 or 2 too many heads. Sure, you could convert one to a laundry room or workshop, but the charter configurations never felt ideal for cruising.

[thinwater]

One. I grew up in a house with one bathroom. No problem. I also cruised with one and don't remember any issues. It's not like anyone is going to take a long shower or bath; that is an important distinction.


We've got 3 bathrooms in our house now. If I'm working in one, the third STILL never get used. I think I could board up the downstairs bathroom and the wife wouldn't notice for a month.


If someone wants a second one, they can maintain it. If it means a second holding tank, they can leap. A second is a total waste, IMO.