dix design cat?

[Mick C]

Wow, I’d love to see Cheetah first hand, it’s the most amazing of the DH550’s. I see it for sale. I’m sure even at least hat price they will both struggle to sell it and it will always be worth more.

Beautiful boat, love the owners hull layout...now that’s an owners hull!

[Catmandu]

Cheetah is an amazing boat that is highly customized and even has a jacuzzi tub in the owners hull! When I first set foot on her the first thought that I had was, “Wow this is way too nice for my kids ... “

Cheetah has been for sale for a while and the price has come down significantly. She is a good deal for a knowledgeable buyer.

[Redreuben]

Dings and scrapes should be taken care of quickly on foam boats too, water pressure at speed can rip the skin off a foam boat before you can say “no claim bonus”.

[UpOnStands]

Originally Posted by Redreuben

Dings and scrapes should be taken care of quickly on foam boats too, water pressure at speed can rip the skin off a foam boat before you can say “no claim bonus”.

This Speed you mention, I hope it is over 25 knots.

[daletournier]

Genuine question. This is an expensive big boat. Why would you choose to build out of ply over foam or Balsa?

[Catmandu]

Let me attempt a genuine answer:

First, people hear “plywood” and instantly think of the plywood they see at the local hardware store. The plywood that is spec’ed for the DH550 is Okoume/Bruynzeel that is NOT your average plywood. It is made from solid laminates of an African mahogany (gaboon) that is very resistant to water incursion and the layers are laminated with epoxy and not your average wood glues.

For the weight, plywood/epoxy construction produces a very stiff structure. Only a full - carbon fiber hull is stiffer but not always lighter. Light and stiff are critical for cats if you want them to sail well.

The highest end Sport Fishing yachts are made out of plywood/epoxy because the boats are ¾ the weight of a cored fiberglass boat of similar size and stiffer/stronger. As such, these plywood/epoxy boats are faster (46+ kts) with engines that are ¾ the size and burn ¾ the fuel than similar sized Vikings see: Paul Mann Custom Boats |

Advantages to plywood/epoxy construction:
- No large up-front tooling costs (plugs/female molds)
- Produces a very light/stiff structure
- Can be built by amateur builders with hand-tools
- You don’t worry about delamination but you do worry about wood rot
- Very easy (inexpensive) to repair with simple tools
- There are now precut kits for the DH550 from Exocetus that will take a lot of time and risk out of the build.
- If you have the time but not the $$ it is way to get into a great world-class cruising cat for half the price of a new comparable cat.
- Some like working with wood better than working with fiberglass

Disadvantages:
- Labor in intensive. Exocetus kits help but you trade off upfront tooling costs for many hours faring/finishing (more labor hours required than female molded boats)
- You have to pay very close attention during the build and make sure that all wood is properly joined and coated
- You have to keep up on maintenance – and cover dings and scrapes and worry about smacking into things – you should worry about smacking into things anyway.
- A plywood/epoxy cat will be harder to sale due to prejudices and lack of knowledgeable buyers. This prejudice is compounded if the boat was amateur built. Prejudice against plywood/epoxy boats does not seem to exist for sport fishing yachts – you pay a premium for these boats.

There are no perfect boats or boat building techniques they are all a set of trade-offs. That being said, some of the nicest casts I have been on are DH550’s built by “amateurs”.

[Catmandu]

Let me attempt another genuine more concise answer:

Our Dh550 is 3-10 tons lighter than other 55' cored fiberglass cats and it is also MUCH stiffer (no creaks, groans or flexing when pushing the boat (10+ kts) in steep seas). It feels and sounds as stiff as an all-carbon HH55 cat (I know, very unscientific comparison).

The DH550 can sail windspeed at 4-10 kts. At 4-5 kts true wind it will sail 4-5 kts but if you add just one engine at 1,800 rpm in these conditions, it will pull the apparent wind forward and move the boat at 9-10 kts motor-sailing.

Light weight is a huge advantage for cats - the DH550 motors at 10+ kts with 54 hp Yanmars. Many 55' cats have 100+ hp motors. It cruises (one engine at 1,800 rpm) at 7.2 kts burning 3 liters/hr of fuel.

Add a structure that is easy to repair and these are some reasons why some will choose epoxy/ply over a cored glass boat - less weight, stiffer boat, cheaper to buy/run/maintain.

[daletournier]

Thanks for your reply, appreciated. Fantastic boat.

[szkutnik]

Hi all,

I have read all the above comments on construction methods for the DH550 with great interest. I too am a big fan of this boat and in fact we have just completed a set of hull moulds for our first build. I am also a big fan of both construction methods, epoxy plywood and foam cored glass/carbon, and as an industry professional I would like to offer my opinion on both types of construction.

There's no doubt that DH550 is a great project, and plywood is a very good choice when it comes to it’s construction.
I would add that I agree with almost everything that Cathmandu has said, except for the last sentence:

"Add a structure that is easy to repair and these are some reasons why some will choose epoxy/ply over a cored glass boat - less weight, stiffer boat, cheaper to buy/run/maintain”

I've been building and repairing yachts for 37 years and my experience doesn't allow me to support the theory that epoxy/ply boats are easier to repair.

Repairs are more difficult especially if maintenance is not carried out on an ongoing basis and water penetrates deeply causing damage. Of course, this is not a problem for people with knowledge of what they are doing. But this is also true of core/glass construction.

To be clear clear about this I am not against ply/epoxy technology. I built several such boats including a 40ft sloop that I built and sailed with my own family nearly 15 years ago. She is a splendid boat, lightweight and extremely stiff and strong and is currently being refitted by her new owner with a circumnavigation in mind. This technology is irreplaceable also in boats of different types such as sport fishing boats, for example.

However, having said all that, my experience has made me sure that foam cored glass/carbon, built by professional boatbuilder with use of vacuum infusion and epoxy resin is the way to go with this particular design.

It will be lighter and stiffer than a ply/epoxy version, but only if the builder in question really knows is job and uses the highest quality materials. But unfortunately, this is not the case of the majority of companies mass producing boats these days using this construction process.
The only thing that matters to these companies is that the boat has an impressive exterior/interior appearance and the company maximises their profits on each build. No one is interested in the performance or seaworthiness of these boats or indeed incorporating high quality materials. These boats are designed to last 3-4 years in charter industry and then sold to new owner who will then be responsible for sorting out the mess.

It my belief that cored glass/carbon is a great construction alternative for those who are afraid of wood as a construction material. Dudley and Phill also designed the epoxy/glass/carbon 57 feet version of the yacht. The moulds for production of this design are now ready and available from aquinus.com.

The DH550 is indeed a magnificently designed yacht whatever construction method you employ. But for those who are concerned about resale value, and lets face it, most potential owners are, plywood as a material for construction will inevitably have a dramatic effect on the resale value of the yacht. For those thinking about a project like this, it is a point that cannot be overlooked. Even with all my experience and respect for ply/epoxy as a construction method, we have still decided to build this current 550 in cored glass/carbon.

[clockwork orange]

Originally Posted by Catmandu

Let me attempt a genuine answer:

First, people hear “plywood” and instantly think of the plywood they see at the local hardware store. The plywood that is spec’ed for the DH550 is Okoume/Bruynzeel that is NOT your average plywood. It is made from solid laminates of an African mahogany (gaboon) that is very resistant to water incursion and the layers are laminated with epoxy and not your average wood glues.

For the weight, plywood/epoxy construction produces a very stiff structure. Only a full - carbon fiber hull is stiffer but not always lighter. Light and stiff are critical for cats if you want them to sail well.

The highest end Sport Fishing yachts are made out of plywood/epoxy because the boats are ¾ the weight of a cored fiberglass boat of similar size and stiffer/stronger. As such, these plywood/epoxy boats are faster (46+ kts) with engines that are ¾ the size and burn ¾ the fuel than similar sized Vikings see: Paul Mann Custom Boats |

Advantages to plywood/epoxy construction:
- No large up-front tooling costs (plugs/female molds)
- Produces a very light/stiff structure
- Can be built by amateur builders with hand-tools
- You don’t worry about delamination but you do worry about wood rot
- Very easy (inexpensive) to repair with simple tools
- There are now precut kits for the DH550 from Exocetus that will take a lot of time and risk out of the build.
- If you have the time but not the $$ it is way to get into a great world-class cruising cat for half the price of a new comparable cat.
- Some like working with wood better than working with fiberglass

Disadvantages:
- Labor in intensive. Exocetus kits help but you trade off upfront tooling costs for many hours faring/finishing (more labor hours required than female molded boats)
- You have to pay very close attention during the build and make sure that all wood is properly joined and coated
- You have to keep up on maintenance – and cover dings and scrapes and worry about smacking into things – you should worry about smacking into things anyway.
- A plywood/epoxy cat will be harder to sale due to prejudices and lack of knowledgeable buyers. This prejudice is compounded if the boat was amateur built. Prejudice against plywood/epoxy boats does not seem to exist for sport fishing yachts – you pay a premium for these boats.

There are no perfect boats or boat building techniques they are all a set of trade-offs. That being said, some of the nicest casts I have been on are DH550’s built by “amateurs”.

While I would agree with most of what you have said, as a boatbuilder and big fan of plywood as an engineering material I would like to point out a couple of errors regarding build methods and materials.

1/ You have referred several times in earlier posts to "cold moulded strip planked wood epoxy" as if it were a build method where in fact they are two separate totally different construction methods, both excellent but different methods, the only similarity being the use of wood and epoxy.

2/ Brunzeel plywood is a brand of plywood manufactured to British standard 1088. The important thing being the BS1088 designation. There are many manufacturers worldwide who manufacture to this standard and as long as they are true to the standard they are equal. The standard specifies such things as veneer quality, number and thickness, both face and inner plies as well as, most importantly the glue line, which is the one thing, you, as a builder cannot visually inspect. Epoxy is NOT used in marine plywood and in fact would not pass BS1088 as it would fail the boil test. Most high quality lightweight plywood boats are built using okoume/ gaboon BS1088 marine plywood due to its light weight alone but it is important to note that it is poor in terms of resistance to decay. As a species it is rated as non durable so it relies heavily on proper build methods as stated in previous posts. There are other species of BS1088 plywood with better durability but they are heavier and would still require the same fastidious build care and ongoing maintainence for a long life.
The best marine plywoods, regardless of species are manufactured to BS1088 with Lloyds certification.
The D550 is a stunning design and it is unfortunate that there is such predudice against plywood. This is especially true in the US where all domestic plywood is garbage and no manufacturer produces to BS1088 so the average joe never gets to see real marine plywood to appreciate what a magnificent material it is.

Steve.

[Teleman]

Exocetus has added a DH 430 to the 470 and 550 kits.

All the same design features in a smaller package, still more than big enough for family cruising.
Would probably cost half of the 550 in both money and build time.

[Mick C]

I reciently had the pleasure of visiting a build of a 470 and it’s a magnificent machine. It’s such a pleasure to see the wood in the build and it’s a real “craftsman” job.
I’m enjoying reading the posts here as it seems to be the first time there has been a genuine discussion about timber versus Fibreglass that hasn’t descended into a ...”mines bigger than yours” rant. Well done all, keepthe info coming.

Mick

[Catmandu]

I appreciate feedback from those that actually make money building boats or have at least built a boat or two.

I love the DH550 design. I love its layout and performance as well as all the thought that Phil Harvey put into it gained from his experience of sailing over 150,000 miles. I describe the DH550 as fast or faster than a Catana/Outremer but with the space of a Lagoon".

While owning one, I have often asked myself what would I do to make it better. Here is a list of things that I would consider:

- Build it out vacuum-bagged cored S-glass/carbon fiber. I spoke to Phil Harvey about this and he said that a build out of carbon would make the boat stiffer (e.g. faster) but not necessarily lighter due to the layup schedule requirements. The stiffness and strength of a carbon version would increase and could accommodate a larger rig. (Our boat was about 13.8-14.1T (loaded with stuff) which is really light for a boat of her size.) The biggest downside to a cored vacuum bagged boat is price. This build approach makes the boat A LOT more expensive to build in terms tooling/molds and material costs.

- I would extend the hulls and transoms at least a meter in order to move the engines out from under the rear berths and trade out the shafts for sail drives (even with the added maintenance) I think it would be worth it when you have to motor. From a maintenance point of view the shafts were easy and having the engine under the berths made it really nice to work on them in inclement weather or out on the ocean if needed. considering the trade-offs, I would still move them back into a separate compartment.

- I would increase the size of the rig - well maybe not. The boat averaged 200-250 nm/day with ease as it was. The one time we sailed her at 14-15kts everyone started whining and yelling to slow down to smooth out the ride. At 8-11kts the boat just whooshes along.

- I would set it up with a sprit for a screecher/asym and four winches (instead of two) to manage a wider range of fore sails to improve its performance off the wind.

If I could get a DH550 in carbon/s-glass/epoxy would I do it - Absolutely if I thought that I would not take a bath on the resale price. I would need $1-$2M extra over a epoxy/ply version but a carbon boat would get me closer to that elusive perfect boat.

So is the extra expense of going vacuum-bagged cored/carbon/glass worth it? Maybe. I was pretty impressed with the performance of the ply/epoxy approach, especially considering the overall bang-for-your buck - I think its really hard to beat.

However, I did agonize about water intrusion into the wood all the time. We did find a section on the rear transom where the wood had to be replace due to a grill mount where there fasteners were just screwed into the wood (this is a BIG no-no). It took seven years of weather, but the water got in and softened an area of about 6"x 12" through those screw holes. The fix consisted of cutting out rotted wood, scarfing/gluing in a replacement piece of oukumi, sanding and painting. The repair took two days mostly waiting for epoxy and paint to dry. For me, this repair seemed A LOT more straightforward than dealing with a sandwich of materials and the challenges that others were having trying to fix cored hulled cats below the waterline.

Here is a question for the builders: It it any different trying to fix water intrusion on epoxy ply boat vs. an end-grain balsa cored boat?

[daletournier]

Originally Posted by Catmandu

I appreciate feedback from those that actually make money building boats or have at least built a boat or two.

I love the DH550 design. I love its layout and performance as well as all the thought that Phil Harvey put into it gained from his experience of sailing over 150,000 miles. I describe the DH550 as fast or faster than a Catana/Outremer but with the space of a Lagoon".

While owning one, I have often asked myself what would I do to make it better. Here is a list of things that I would consider:

- Build it out vacuum-bagged cored S-glass/carbon fiber. I spoke to Phil Harvey about this and he said that a build out of carbon would make the boat stiffer (e.g. faster) but not necessarily lighter due to the layup schedule requirements. The stiffness and strength of a carbon version would increase and could accommodate a larger rig. (Our boat was about 13.8-14.1T (loaded with stuff) which is really light for a boat of her size.) The biggest downside to a cored vacuum bagged boat is price. This build approach makes the boat A LOT more expensive to build in terms tooling/molds and material costs.

- I would extend the hulls and transoms at least a meter in order to move the engines out from under the rear berths and trade out the shafts for sail drives (even with the added maintenance) I think it would be worth it when you have to motor. From a maintenance point of view the shafts were easy and having the engine under the berths made it really nice to work on them in inclement weather or out on the ocean if needed. considering the trade-offs, I would still move them back into a separate compartment.

- I would increase the size of the rig - well maybe not. The boat averaged 200-250 nm/day with ease as it was. The one time we sailed her at 14-15kts everyone started whining and yelling to slow down to smooth out the ride. At 8-11kts the boat just whooshes along.

- I would set it up with a sprit for a screecher/asym and four winches (instead of two) to manage a wider range of fore sails to improve its performance off the wind.

If I could get a DH550 in carbon/s-glass/epoxy would I do it - Absolutely if I thought that I would not take a bath on the resale price. I would need $1-$2M extra over a epoxy/ply version but a carbon boat would get me closer to that elusive perfect boat.

So is the extra expense of going vacuum-bagged cored/carbon/glass worth it? Maybe. I was pretty impressed with the performance of the ply/epoxy approach, especially considering the overall bang-for-your buck - I think its really hard to beat.

However, I did agonize about water intrusion into the wood all the time. We did find a section on the rear transom where the wood had to be replace due to a grill mount where there fasteners were just screwed into the wood (this is a BIG no-no). It took seven years of weather, but the water got in and softened an area of about 6"x 12" through those screw holes. The fix consisted of cutting out rotted wood, scarfing/gluing in a replacement piece of oukumi, sanding and painting. The repair took two days mostly waiting for epoxy and paint to dry. For me, this repair seemed A LOT more straightforward than dealing with a sandwich of materials and the challenges that others were having trying to fix cored hulled cats below the waterline.

Here is a question for the builders: It it any different trying to fix water intrusion on epoxy ply boat vs. an end-grain balsa cored boat?

I'm not even close to being a builder yet I've owned a ply wood boat and a balsa boat.

I think the difference (theoretically) is the water can run with the plywood effecting larger areas. The balsa being end grain should isolate the water damage unless we are talking delamination.

I've cut out large sections of ply. In saying that this was due to exactly what you described, a previous owner not over drilling holes and filling them with epoxy and then fastening through the new filled hole.

I would buy this plywood boat in a heart beat, money permitting.

[clockwork orange]

Both plywood and balsa cored boats are fairly easy to repair and both require the same preventative measures to prevent ingress in the first place but when water does get in to a balsa cored boat it spreads far and the core turns into compost. The fact that it is end grain does not slow it down a bit. I have infused with contour balsa and all the individual blocks get surrounded by resin an im sure this would isolate the damage but have not done tests to confirm this belief but of course it would be heavier. Plywood is a wonderful engineering material.