Chetzemoka - a multi-purpose outrigger for the Salish Sea

01 January 2015    Editor    37 Comments

Chetzemoka is the latest draft on an idea that has been slowly brewing for some time - a small multi-purpose cruiser/cargo/expedition vessel designed for the Salish Sea. It’s a motor sailor, because the wind rarely blows when you’d like it to in these parts, but you still want to be getting where you’re going. A 15-25 hp outboard will get the job done, with some wind assist via the rig.

Initial inspiration comes from the ubiquitous Filipino double outriggers, called paraws or bangkas, that handle everything from fishing to water taxi service in the Philippine Archipelago. They are a wonderfully versatile and efficient design, and even though we lack the plentiful bamboo that is used for much of its construction, this stitch and glue plywood version shares a lot of the same DNA. She is light and narrow for her length, and stability is achieved not by a weighted keel or a form stable hull, but by widely spaced outrigger hulls, or as Jim Brown says: “live buoyancy to leeward!”

Being mostly a power boat, she has no use for the high buoyancy amas of a typical modern sailing trimaran. Like the bangka, her amas are low buoyancy and low freeboard, and barely kiss the water when at rest. This saves weight, windage and drag compared to a full-on sailing vessel.

The hull shape is a simple sharpie skiff, with a medium load displacement of 3200 lb.

For accommodations, Chetzemoka has a most powerboat-like feature: an enclosed pilot house! The aft cabin includes most of the features of a long haul trucker: steering wheel, double berth, mini galley, beer cooler, and CB radio or iPhone. Forward is a 6’ exterior cockpit or cargo bay, with good storage below the sole. Forward of the cockpit is the head (where the Admiralty intended it) and a shallow bow cockpit for anchoring and attending to mast raising and lowering. The aft helm position gives good visibility of the rig when under sail. Borrowing again from the bangka, the design features wide side deck extensions that permit safe crew movement going fore and aft.

The crab claw rig is optimized for reaching and off-wind courses, and a centerboard is not even specified. It’s just so much quicker and easier to power to windward that it makes little sense to spend time and money on windward sailing devices like foils and expensive rigs. This 250 sq. ft. crab claw can be made from a flat sheet of poly-tarp if need be. There is no standing rigging, sail tracks or slides, battens, winches, or any number of items that contribute to a modern sloop’s considerable expense. The free-standing mast is only 19’-6” long and with the tabernacle it folds down to a bridge friendly air draft of 8’. That said, Chetzemoka should still be quite fast under sail with a SA/D ratio of 18.5. It would be an interesting experiment to try anti-vortex fins or “chine runners” to see if the sharp chined hull can be induced to sail to windward. There would be plenty of times when sailing while motoring would pay off with fuel savings, and I imagine the spreadsheet involved with calculating the optimum combinations of throttle with various wind speeds and headings could make a navigator geek very happy.

Even though the rig is simple, the boat is still fairly complex thanks to the outriggers, something that cannot be avoided. However, they do provide excellent kayak or dinghy storage. It wouldn’t take much argument to remove one ama and make do with a single outrigger. It would save weight, windage, overall beam, expense and build time. However, I have to say that there is something mighty pleasing about bilateral symmetry.

Chetzemoka is an evolving concept, and feedback is welcome. An intriguing thought is that when the design is scaled up to 38’, full standing headroom is available throughout.

Chetzemoka Particulars

  • LOA: 28’
  • BOA: 17’-3”
  • Hull beam: 4’-7”
  • Draft: 1’-4”
  • Sail Area: 250 sq. ft.
  • Displacement: 3200 lb
  • SA/D ratio: 18.5
  • Bruce #: 1.08

 trimarans / new designs 


37 Comments

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02 Jan - 00:31

Paul CHEEVERS

Hi Michael, Give me the tropical version and I will start building tomorrow! Seriously though I think that the pacific island community would be interested in this design style. So far all the current modern/tradional style boats designed and delivered have a price tag of $500,00 plus. Not exactly available for the grass roots.

02 Jan - 05:44

Peter Mirow

Nice, unconventional design! Good job.

02 Jan - 13:15

Laurie McGowan

Great idea, Michael! Looks really cool, easy and inexpensive to build, and fun to sail!

02 Jan - 15:18

Chris Luomanen

I love the work-boaty feel of this. It reminds me of Tom Jones' Buy Boat, seen though a southwest pacific lens. There's a volkscruiser-esque elements to the overhanging side decks with bulwarks. I like the access and spray reduction they bring. Maybe a pivoting leeboard could be fitted for upwind duty? Or maybe I'm overthinking it. Lovely work, as usual, Michael

02 Jan - 20:00

Editor

Thanks for the comments! Paul: I think the Filipinos have it all figured out and don't need no stinking plywood! grin Peter and Laurie: thanks guys. Chris: Thanks for the feedback. I'm sort of going for a Down-east x South Pacific mash up. Certainly, a board of some kind could fit, and turn it into a proper sailboat. There is a reason that the native PNW canoes are all paddled and not sailed, and it's not because they didn't know about sails.

03 Jan - 02:16

Paul Cheevers

You could be right about the plywood Michael. Maybe the main hull could be built like the one in the FAO book "How To Build A Timber Outrigger Canoe", by Olaf Gulbrandson? I still would use the plywood amas as these are a big improvement on the vee shaped amas of most FAO designs.

05 Jan - 02:31

James

Elegantly done, Michael. It is simple and practical and, no doubt, would be excellent value for money if and when built.

13 Jan - 10:40

Rudolf van der brug

This design is very goodlooking. It reminds me of Bolger's breakdown schooner. I would love to live on boat like that but I don't want a monohull. You mention the thought of scaling up, I would like to see a larger version. Somehow the single outrigger seems very practical, especially for coming alongside. Rudolf

14 Jan - 16:43

Dave Culp

Outstanding design, Michael. You're aware of my interest in Bankas; I have no hands-on experience at all, but from reading and "arms-length" troubleshooting, I'd say this: Go as narrow on the waterline as you dare, to maximize mileage and speed under power. In which case the boat's going to squat a bit--this is the usual speed limiter on trad bankas. So maybe immerse the transom a bit, or widen it a bit, or both. Go for a little bit of dynamic lift/planing. It seems that ~32' trad boats with ~20-25 horse air-cooled inboards claim 12-14 kts at cruising throttle and outrageous mileage claims (.5 - 1.0 gph). They're longer and heavier than you will be. Bottom line, I think I agree with your choice of outboard, but would look hard at those air-cooled 2 cylinder inboards; they're available anywhere wrecked out of gen sets, water pumps, etc. If a scrapped one can be made to do well, go buy a brand new one and swap it out. If the scrapper doesn't work out, not much is ventured. Yu can get one brand new for $1000-1200 non-marinized, maybe buy the shaft and seals in the Philippines. With the right prop, you should manage considerably better speed--and far better mileage. Cool boat. I like this one a lot!

16 Jan - 09:10

claudio

Brother M... Awesome concept! Well thought out and (as always) amazingly drafted! I love the simplicity of it all.The "outboard/overhanging" seating and cabin is inspired! Very cool. My "Zen" take on it would be... What's the extra outrigger for? Why not 24 or 32 ft.? Would save a few cuts. Dave is right about the back end of skinny hulls (any hulls for that matter) squatting under power.Another location for the motor perhaps? Anyway...thanks for more sleepless nights. Lagoons...coral reefs...grass skirts... Aloha to All claudio

17 Jan - 11:39

Editor

Thanks for the continuing comments! Dave: In fact, the hull transom is immersed a few inches and the max WL beam is carried quite far aft, making a better power boat than sailboat, but that is the design brief. This will also carry the weight of the outboard and fuel, help prevent squatting, and reduce hobby horsing. The air cooled inboard is an interesting idea. Claudio: I actually began at 24', but it grew a bit. As the design develops, I may opt for 24' and 32' versions and skip the 28. Why two outriggers? Well, I am banking on the collective wisdom of the bangka builders, and sticking with their basic paradigm. They think two are necessary.

19 Jan - 08:25

claudio

Aloha Michael, Here's a gem of an article on bangkas... http://duckworksmagazine.com/03/r/articles/banca/index.htm Re the twin outriggers... The twin outriggers on the trad boats make sense because the main hull is always very deep V and therefore has no "stand up" ability. Your version,with a sharpie type hull, eliminates that issue. I'm just wondering what the bottom/sides of Cheta look like? Could you please share some of the basic dimensions/shape of the hull (bottom width/flare of the hull sides/etc.)? I look forward to getting a better understanding of your vision with this, because it's the kind of craft that holds so many possibilities. btw...the Thai version of these type of craft always used the fan tail, longshaft drives. The best way to prevent that rear end squat, I guess. Cheers for now claudio

19 Jan - 18:50

Dave Culp

I share Claudio's interest in this boat's lines. wink I agree with everything Michael says; in addition, I'm impressed that you moved the amas forward a bit--so they aren't involved with any squatting of the main hull under power. You said "Why two outriggers? Well, I am banking on the collective wisdom of the bangka builders, and sticking with their basic paradigm." Probably shouldn't mess with tradition--but I wonder... Whenever one looks at widely varying displacement--the design brief said, "cruising/cargo/expedition"--Whenever one adds variable displacement to a double outrigger, it either must rock side-to-side when empty (amas above the water at rest), or else must carry a lot of the whole boat's mass when heavily loaded, not a great drag picture. We see this in offshore trimaran powerboats--usually solved with powerful and expensive variable immersion schemes for the amas. Cool thing about a single outrigger is that it automatically adjusts for displacement/depth of main hull, just by rotating a couple of degrees, keeping vaka/ama displacement ratio optimal. There are lots of compelling arguments for a double outrigger in a sailing vessel, but IMO, a single outrigger might be better for power. Hmmm, which raises the question of when to consider a motor sailor more of a motor boat or more of a sailboat? wink

19 Jan - 19:58

Editor

Hull BOA (not including deck extensions" is 4'-8". WL beam is 3'-2". Bottom beam is 2'-6". In other words, a long and stretched out outboard skiff. I think it would be a bit tender without outriggers, especially with the 'claw, so I won't call it an inherently stable hull. It requires support. This discussion could easily lead to an examination of just when is a slightly wider monohull better overall than an outrigger, if building price and complexity are factored in. Not to mention docking, trailering etc. But then I'd be showing monohulls on Proafile, and we have our limits. In real life, the sailing rig is an affectation. I have no doubt that like every other "sailboat" in the PNW, it will spend its life motoring from here to there, with occasional sails when the mood is right. However, the sailing rig helps to "keep it real" and points me toward low power, low drag solutions, rather than just solve every problem with a bigger outboard.

21 Jan - 02:28

James

An extra 4 feet in the cabin area to give 32' overall would greatly enhance the livability of an already practical design. A bimini over the cockpit with drop down clears would top it off nicely, I think. If it were mine, I'd go with the outboard for simple practicality even though it might not be in the best position performance-wise. It is easily accessible for servicing/maintenance and repair. It could be used for steering the boat in tight marina positions where you might be surrounded by potentially expensive insurance claims! Folding amas would be handy in marinas, too, as well as for trailering but perhaps that is starting to get too complicated. Whatever, I think this design is worth pursuing some more, Michael.

21 Jan - 08:12

claudio

Hi Michael, Thanks for the added info. A sharpie with a 2.5 ft bottom width would have to have sides 1 ft high max...with no topsides...in order to stay upright. So now I see why you want the outriggers. This would be a fast, fuel-sipping boat for sure. I'm with James with regards to the extra 4 feet. Would make the build quicker, easier and maybe even cheaper. These boats are also commonly referred to as "pump boats", because they would mostly use a simple 5.5 h.p. (or bigger) generic motor used for running well pumps, irrigation pumps, etc., attached to a longtail shaft...Thai style. Very cheap in those countries. But...getting in and out of marinas ( as James mentions)...would be "entertaining" to say the least. If an outboard was the go, I would mount it to the aft beam. That would go a long way to minimizing the squatting at wot. I still don't see the reason for the extra outrigger! Maybe I'm just too lazy a builder! : ) Enjoying this thread, Cheers claudio

21 Jan - 19:31

Editor

Thanks for the continued interest! Regarding the great 1 ama vs. 2 debate: For the Salish Sea and probably anywhere except in the trade winds, the double is the winner for fuel economy. Reason is that the main hull is much more efficient of wetted area than the outriggers for a given displacement, so having two collectively heavier floats barely skimming the water will cause less drag than 'dragging' one ama that must be well immersed. When the boat is well heeled under strong winds, even under power, it is probably a different story. But we’re not looking for Vmax under those conditions. Also, if Chet is to fold for trailering, then the trimaran configuration would be preferred. However, the differences would be of a small degree and the advantage would switch from sea condition to condition, with the single better in some conditions, and the double better in others. It would be fun to have both configurations sailing in company to compare. Squatting is generally caused by a hull being pushed harder than it was designed or by poor weight placement. If both the HP and the weight are known, then the proper, no-squat hull can be designed to match. As far as alternative engines, I’m all for them (even whirling blades of death Thai longtails), and someone else can do the experimenting. Until then we’ll be using outboards.

23 Jan - 22:06

Valéry Gaulin

Nice design!!! It make me want to build my next trimaran. I also love the concept of Trimaran MotorSailor. I am thinking that it could be my next project after I am completely done with my small electric aluminum trimaran motorsailer project. I might be tempted to suggest a lug yawl sail plan for ''CHETZEMOKA'' similar to '' ROMILLY'' sail plan. What do you think about it? Yawl sail plan seams to be great for motorsailer. It can balance the helm while sailing and the mizzen is always useful when motoring. Anyway awesome design!!! do you have a plan showing the accommodation arrangement inside the cabins?

28 Jan - 15:33

Editor

Hi Valéry, thanks for the comment. I am a fan of lug rigs and I don't see why a lug would not work as well. Why is the mizzen useful when motoring? I will update this post with more images as time allows (slowly).

29 Jan - 18:07

Valery Gaulin

First I am not an expert or do I have much experience! On a motorsailer a Mizzen sail will help to cancel rolling when there is too much wave. Of curse rolling with a trimaran motorsailer might not be a big problem but the mizzen might give more confort. Second a mizzen sail will always keep you facing upwind at anchor. A mizzen will also help you to keep facing upwind also when raising the mainsail. A mizzen will help balance the helm when motorsailing. A mizzen sail can always help you to steer the boat when in trouble. I just think that the pros of a mizzen sail out weight the cons of not having one, especially when it is not intended to be used with a racing sailboat. Anyway this is just my opinion! Be carefull my opinion is mainly based on reading and my small experience with my cat ketch trimaran.

11 Feb - 08:23

Nathaniel S. Ramirez

Hello, Michael, Very nice take on our Philippine Banca design. I would not be surprised to see a few of these in Philippine waters in the future. In fact, I do not mind to be one of the first to build your design here in the Philippines. How much for the study plan for this one? Let me know. Thank you.

11 Feb - 10:37

Editor

Nathaniel, thanks you for the comment, it's nice to get affirmation from the Philippines! I do not yet have study plans, but as the design progresses I will post updates here.

11 Feb - 18:39

Valery gaulin

Yes me too I want the study plans. Let me know when it is available

11 Feb - 20:17

Nathaniel S. Ramirez

Hi, Michael, alright that will work. Will be working of the larger design too. Because that might be the right size for me. Either a 32' or the 38' with the full height cabins will do. Are you by any chance in the PNW. Maybe around PT. I lived in Silverdale for 16 years, then went to PNSWB in Port Hadlock. As far, as your Chetzemoka design. I even like your color palette. That is how much I like it.

12 Feb - 07:44

Editor

Yes, in Port Townsend!

12 Feb - 12:55

Nathaniel S. Ramirez

Michael, I found out about Chet in a DIY Forum called PHBYC(Philippine Home Boatbuilding Yatch Club). It was shared by Pere Caracol. Here is the linkhttps://www.facebook.com/groups/pinoyboats/10153086128727235/?notif_t=group_comment_reply A lot of the members liked your design. Maybe you can use the membership as a sounding board in the design process. I am sure they would love that. By the way, PT is one of my favorite places to have lived in, if only for a little while. Lived there in 2010. I still own a piece of land there, so I might still settle down there someday.

12 Feb - 13:03

Nathaniel S. Ramirez

Michael, Here are the excerpts from our message exchange. Me Love this design. I think I found a good starting point for a first Philippine build. Thanks for the share, Pere Caracol. Without it I would not have seen this excellent take on the Philippine Banca. Its exactly what I need and looking for. PereI´m happy you like it Nathaniel. Its designed for cold waters but I thinks can be "tropicaliced" easily for Philippine waters. For me I will eliminate the stern cabin to make a second cockpit and both with big bimimis. This bimimis can be converted to "cabins" with some canvas work, especially if bimimis are made of the PVC canvas used in cargo trucks (watertight canvas). Will be great for parents with childs to have two cockpit ! MePere, this is just fine for the Philippines too. Its not always warm out at sea specially when there is a storm brewing. Which happens a few times each year. Besides, I will probably be sailing her across the Pacific to the Pacific Northwest from time to time. In the Salish Sea where Michael lives and where I studied Large Craft Wooden Boatbuilding at the Northwest School of Wooden Boatbuilding in Port Hadlock, WA near Port Townsend. I use to live in Silverdale, WA near Bremerton across the Puget Sound from Seattle, for 16 years until 2012 when I returned home. So my preference is to extend the forward cabin and probably prefer the 38'version with full height that Michael is planning. Because I have back issues. But your idea of a bimini top and no stern cabin will probably work for most people here. All the above, a lug sail and inboard diesel engine would make me a happy sailor.

12 Aug - 07:03

Wolfengott

Hello Michael, With a few modifications in mind, i think this would be a perfect banca to built. Would you have any updates on the design or actual build?

12 Aug - 09:36

Editor

Thanks for the ongoing interest in Chetzemoka. I am currently doubling down on yacht design school, and when I'm finished this boat will be first in line to get some plans drawn up. However, that won't be for at least another year.

14 Aug - 03:30

Nathaniel S. Ramirez

Michael, which Yatch Design School are you attending?

14 Aug - 12:50

Editor

Westlawn Institute of Marine Technology. http://www.westlawn.edu

29 Dec - 00:46

Nathaniel Savella Ramirez

Westlawn is a good one. I cannot wait for your plans.

07 May - 23:03

Kristine B.

Good evening Michael, I was looking at Chetzemoka, I have to say nice looking design. I agree, here in northern Puget Sound most of the time sail boats are motored more than sailed, because when the weather is nice the winds are fickle most of the time. At least here in the San Juans. I could see building the Chetzemoka as an outboard cruiser with 9.9 high thrust outboard, with a hull speed of around 6.6 knots you would get 5 or so knots with the 9.9 running a little over half power so your fuel burn would be about 1/2 gallon an hour. I would say that's not bad at all. Dave Culp's idea of pushing it out to about 32 feet is not a bad idea. The idea of using an inboard not a bad idea other than it would increase the boats draft by foot or more. The idea of an air cooled motor, I don't know most are vee-twins so it's something more to get around in the narrow cabin. A 25 hp high thrust outboard would push this boat up to hull speed even at 32 feet that would be 7.1 knots with a easy cruise of 6 kt. Anyway Blessings All Kriss

08 May - 10:21

Editor

Thanks for the comments, Kriss.

09 May - 21:04

Nathaniel S. Ramirez

Michael, How is Yatch Design School proceeding. How about the study or building plans for the Chetzemoka. Its almost time to start building the boat here in the Philippines.

18 May - 18:44

Ray

Wow! And I thought I had looked everywhere. Michael, are you still doing design work? If so, I would love to get in touch with you.

10 Jul - 01:06

Jackson

Caro Michel, sou do Brasil, sou pescador gostaria de adquirir o projeto do Barco, acho que é o futuro para pequenos pescadores profissionais.