Podcat - anybody have any experience?

[markiobe]

No I didn't know what one was either 😅.

For the uninitiated, a podcat is a catamaran but with no accommodation in the hulls, all of the accommodation is on the bridge deck. There seem to be some really big advantages in theory and I'm interested to see if anyone has any experience. The pros/cons as I see them are:

Pros:
- finer hulls therefore much more easily driven
- safer as you can have smaller rig and the hulls are easily be driven through waves, less chance of 'tripping' downwind
- lower hulls, no need to accommodate a standing person therefore much less windage. Also lighter and simpler to build. We would be looking at 1.3m keel to deck
- reverse bows with narrow hulls will act as wave-piercers, smoothing out the motion
- you can build a longer boat for the same cost/weight thus improving the motion and speed even more
- better weight distribution, you can place all of the heavy objects, (tanks, engines etc) right in the centre and really low down as you have no need to worry about space for humans to walk around

Cons:
- less privacy as you're not in a separate hull from any guests you might have
- less interior storage space for an equivalent size boat. Tons of storage space in the hulls, however accessed from the top only
- resale value as it's out of the ordinary

Obviously this would be a really poor design for a charter cat, but for a liveaboard it seems to be a really good option. However I've seen virtually none out there apart from some very weird looking, very old attempts.

Any thoughts welcome but I'm really interested in experience if anyone has any 👍🏻

[Tupaia]

Derek Kelsall designed a couple of these.
Catamarans - Kelsall Catamarans - KSS FK49 (FastKat)
Catamarans - Kelsall Catamarans - KSS 39 Coral


Better than an open bridge-deck cat as all the accommodation is in one place. On an open bridge-deck cat what ever you want is always in the other hull, when it is raining.


Reverse bows tend towards being very wet this could be made worse by the low forward freeboard and pod arrangement.



The anchor set up can be a challenge, no forward apron lockers so the anchor locker (smelly box) tends to be inside the accommodation.



Propulsion is nearly always outboards.



As you say fast and light but very limited accommodation.

[valhalla360]

A lot depends what size and purpose.

I would disagree that the configuration by itself does some of the things suggested. You have to consider the overall design and intended purpose:
- By the time you get up to 40ft, you can have pretty fine hulls while allowing enough room to walk in them.
- Rig size is about the amount of performance you want.
- 1.3m keel to deck on the hulls, means you will likely bury them in rough weather if they are fine. At best, it may mean a wet ride. At worst, your tripping benefit is the opposite.
- For the same accommodations, it not likely to be cheaper as it will need to be much bigger overall.
- Engine access in particular shouldn't be hard to get to. If it's difficult, maintenance tends not to be done.
- A crawl in cabin doesn't make for a great liveaboard option and if you make it full standing headroom, windage could actually be worse than a more traditional design.

Some of the smaller wharam designs do this. They have their adherents but most of the love seems to be from those who can't afford much more.

Assuming yo aren't trying to stay at marinas, a better approach in my mind would be to take something like a 40ft design and stretch the hulls by 4-6ft on the stern and 4-6ft on the bow, narrow them up a bit and keep everything else the same. Once the design and molds are complete, it will cost almost nothing extra to construction but will be significantly faster as LWL is probably the biggest determinant of speed but with the extra length, you not only get extra length but can narrow up the hulls a bit, substantially increasing speed (no need to increase the beam if you keep the rig the same).

Why isn't this done? Most new boats aren't bought by folks heading offshore. They wind up in marinas, where an extra 10ft is a 25% increase in slip fees, haul out, bottom paint, etc.... I have seen a couple attempts where the stern sections actually fold up, so when you come into a marina, you can claim a shorter length...but I've never seen them in real life.

[markiobe]

1.3m keel to deck on the hulls, means you will likely bury them in rough weather if they are fine. At best, it may mean a wet ride. At worst, your tripping benefit is the opposite.

Errrr, no. Wave piercing hulls are an established design in catamarans and make going through waves a design feature. They reduce the chance of pitchpoling as the hulls are so easily driven that they will go straight through the wave and come out the other side. You're right in that if wavy it will be wet but why is that a problem since it turns out that boats are built to be waterproof from the front...

A crawl in cabin doesn't make for a great liveaboard option and if you make it full standing headroom, windage could actually be worse than a more traditional design.

Not sure you read very well, the design has no accommodation in the hulls.

windage could actually be worse than a more traditional design.

Huh? Windage is dramatically less simply because the hulls are lower, most catamaran hulls will be at least 2m keel to deck. For a given design it's purely a function of surface area, lower hulls = less windage.

Engine access in particular shouldn't be hard to get to. If it's difficult, maintenance tends not to be done.

Agreed. The plan is to use outboards which have a clever lifting system so when not in use pivot up into the hulls, replaced by a 'plug' that fills the hole leaving a completely clean wetted surface. The pivoting system also allows for easy access for maintenance.

Assuming yo aren't trying to stay at marinas, a better approach in my mind would be to take something like a 40ft design and stretch the hulls by 4-6ft on the stern and 4-6ft on the bow, narrow them up a bit and keep everything else the same. Once the design and molds are complete, it will cost almost nothing extra to construction but will be significantly faster as LWL is probably the biggest determinant of speed but with the extra length, you not only get extra length but can narrow up the hulls a bit, substantially increasing speed (no need to increase the beam if you keep the rig the same).

Completely agree with your thinking, in fact I had some discussions with a naval architect to discuss exactly this kind of design. Still might be the choice however based on the space we need I like the podcat option better, I think we can get a lighter design that sails better, not only because of the weight but also because of the easily driven hulls.

Why isn't this done? Most new boats aren't bought by folks heading offshore. They wind up in marinas, where an extra 10ft is a 25% increase in slip fees, haul out, bottom paint, etc.... I have seen a couple attempts where the stern sections actually fold up, so when you come into a marina, you can claim a shorter length...but I've never seen them in real life.

Agreed. This is the only disadvantage I can see. Our plan would be a 15.7m hulls (51ft) which gives us about the same amount of storage as a 13m normal catamaran for almost definitely a cheaper price. We get a dramatically better boat from a seaworthiness perspective at the cost of higher marina and haul out fees, but since we plan to cruise full time, shouldn't be a major issue.

In addition most people won't even question the accepted wisdom and will buy a Lagoon, Leopard, FP or similar without questioning whether it is the best boat for their particular needs. The herd mentality is alive and well.

[valhalla360]

Originally Posted by markiobe

Not sure you read very well, the design has no accommodation in the hulls.

Huh? Windage is dramatically less simply because the hulls are lower, most catamaran hulls will be at least 2m keel to deck. For a given design it's purely a function of surface area, lower hulls = less windage.

Never said it did. If the accommodations are on deck, that limits the available height...unless you make for an unusually tall deck structure. So take your pick crawl in accommodations or high windage.

Agreed. The plan is to use outboards which have a clever lifting system so when not in use pivot up into the hulls, replaced by a 'plug' that fills the hole leaving a completely clean wetted surface. The pivoting system also allows for easy access for maintenance.

Your original post suggested keeping the weight down low in the hulls and specifically mentioned engines. Your plug system sounds complicated and prone to failure. Just use a lifting mechanism like most outboard powered cats and keep the motors on the bridge deck.

Agreed. This is the only disadvantage I can see. Our plan would be a 15.7m hulls (51ft) which gives us about the same amount of storage as a 13m normal catamaran for almost definitely a cheaper price. We get a dramatically better boat from a seaworthiness perspective at the cost of higher marina and haul out fees, but since we plan to cruise full time, shouldn't be a major issue.

In addition most people won't even question the accepted wisdom and will buy a Lagoon, Leopard, FP or similar without questioning whether it is the best boat for their particular needs. The herd mentality is alive and well.

A 51ft wharram style boat is not going to have anything close to the accommodations of a more traditional style 43ft cat. Probably closer to a 30ft cat if you don't allow for accommodations in the hulls.

[GRIT]

Sorry, I've no experience with pod cats, but I do find them interesting.

Here's a beauty for you. It's the first podcat of that size I've seen, that isn't made for daycharter.
It's a lot bigger than the 51 feet you planned, but there may be ideas you can take from it.

https://www.yachtworld.com/boats/200...an-72-3512312/

And here's a charter design in your size range, from Kurt Hughes. The hulls are quite narrow, which won't bother you, and you could easily build a pod in lieu of the large roof he's got there. You could easily have him lower the height of the hulls if you like.

http://www.multihulldesigns.com/desi.../yb48chcat.htm


Cheers.
Paul.

[markiobe]

Thanks Paul, interesting! We'll have a study and see if there are ideas to take from them :-)
Cheers, Mark

[markiobe]

Never said it did. If the accommodations are on deck, that limits the available height...unless you make for an unusually tall deck structure. So take your pick crawl in accommodations or high windage.

Apologies, I misunderstood, I thought you meant accommodation in the hulls. The plan would be to have all of the living space including 2 berths on the bridgedeck but even then the windage is lower than a trad design as the salon roof height would be the same as a normal cat (to allow people to walk around as normal), just mounted on lower hulls, so the boat overall would be lower therefore less windage.

Which also brings another benefit into play that I hadn't thought about until now: this design would also lower the C/E of the sail plan, which for a cruising design is a definite safety advantage.

Thanks for the comments and interest. If we end up getting it built it I'll post designs etc so that you can see what it will be. There's also a really unconventional, interesting rig design planned ;-))

[dafid]

This is interesting - somewhat like a pod mounted on the crossbeams of a large cat.

The reduced windage is because the hulls have reduced height above the water...

The wave piercing bows clearly make sense, on a performance cat with a tiny pod/or no pod - boats built this way win races!!

A standing height, living room sized pod is not going to be very wave piercing however...

The standard advice for bridge deck clearance is 30" /0.76metres.
( I think it relies on the boat going over the waves - not through them. )

https://www.researchgate.net/publica...cal_techniques
This study of the waves in the Med , includes satellite observations of swh = "significant wave height" (and lots of other stuff that goes over my head)
//DIRECT quote
Table 3 Monthly swh values for the percentiles of the satellite data for the area of Levantine
Percentile Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Overall
Min 0.30 0.38 0.35 0.19 0.11 0.19 0.27 0.35 0.26 0.13 0.29 0.28 0.26
5% 0.52 0.69 0.54 0.38 0.27 0.37 0.45 0.53 0.49 0.25 0.44 0.38 0.44
10% 0.63 0.77 0.62 0.41 0.34 0.42 0.54 0.59 0.54 0.29 0.50 0.47 0.51
25% (Q1) 0.86 0.98 0.86 0.52 0.41 0.53 0.68 0.71 0.64 0.36 0.64 0.83 0.67
50% (Median) 1.20 1.43 1.33 0.71 0.52 0.69 0.83 0.82 0.85 0.53 0.96 1.22 0.93
75% (Q3) 1.60 2.09 1.68 1.30 0.73 0.82 1.06 0.92 1.05 0.73 1.28 1.67 1.24
90% 2.05 2.48 2.12 1.53 1.27 0.94 1.22 1.04 1.27 1.04 1.69 2.08 1.56
95% 2.17 2.84 2.38 1.71 1.88 1.01 1.31 1.13 1.36 1.22 2.48 2.54 1.84
Max 3.29 3.53 3.07 2.28 2.94 1.41 1.73 1.37 1.65 1.40 4.02 3.12 2.48
//End quote
But a wave of 4 Metres that hits the pod with 3.25 metres of water would be EXTREMELY unpleasant.

Even a 90% wave (ie 1 in 10 waves) that hits with between 20cm and half a metre of water during the summer sailing season would be unpleasant.



Note: there are two things that confuse me...
1) Since the area under study is large you would be EXTREMELY unlucky to hit the maximum wave height (from Wiki) "The Levantine Sea covers 320,000 km2 (120,000 sq mi)."

2) The https://en.wikipedia.org/wiki/Significant_wave_height explanation, suggests that if you are in a wave distribution with the SWH = 1 metres, then 1 in 10 waves will be higher than 1.07 metres, 1 in 100 will be higher than 1.5 m and 1 in 1000 higher than 1.8 metres.

A marine architect would probably be able to make sense of this.

[44'cruisingcat]

No personal experience, but a good friend did a 1000 mile passage on B-52, a 52 foot podcast. He was very impressed! Wanted to build one. The big advantage is you can have a very large "footprint" very cheaply. Long hulls and long crossbeams cost very little. For it's footprint it should be very light too, and easily driven, so a reasonable size rig and sails will work well.

Another advantage that may not spring to mind is that you can use a household toilet!

The big downside would be similar to what most trimarans have: very high marina costs for the accommodation offered.

[markiobe]

No personal experience, but a good friend did a 1000 mile passage on B-52, a 52 foot podcast. He was very impressed! Wanted to build one. The big advantage is you can have a very large "footprint" very cheaply. Long hulls and long crossbeams cost very little. For it's footprint it should be very light too, and easily driven, so a reasonable size rig and sails will work well.

Interesting! Do you a link or any other info about the boat? Searching on B52 either gives me long range bombers or slightly out there 80s bands.. :-))

[markiobe]

The standard advice for bridge deck clearance is 30" /0.76metres.
( I think it relies on the boat going over the waves - not through them. )

I think you're probably right :-)).

This is one of my biggest questions as obviously you need to balance the wave-piercing nature of the hulls with the comfort of the ride. The plan is that the designer/builder will build one for himself to see how it works and we'll get to sea-trial it before making a decision. There are a number of critical questions of which this is clearly one. Thanks for the info, will do some research on this...