Full Displacement of semi

[Portager]

OK, Will, here is a post from Michael Kasten to the Trawler List http://lists.samurai.com/pipermail/t...il/031596.html Sat Apr 14 11:56:10 EDT 2001.

“TW Listees,

Patrick Gerety has forwarded some recent TWL messages re: the relativecosts of a CPP installation vs an equivalent FPP installation. This question is brought up sufficiently often that I have made the following actual cost comparison.

In so doing, it's possibly best to make this kind of comparison using equipment that is suited to the requirements of a specific engine. Let's say the Lugger 6 cyl turbo: the Lugger 668-T.

CPP: Controllable Pitch Propeller Equipment

Sabb HVP 65-E as of 1999 was quoted at 60,000 NOK, ex works Bergen, Norway. At that time they were quoting a 20% discount for direct orders. The exchange is currently USD $1.00 equals NOK 9.08. This translates to a cost of USD $5,286 assuming the NOK price has not changed much, and assuming the same direct order discount remains available.

The completely assembled Helseth 60mm shaft, stuffing box, stern bearing, shaft tube, and 660mm 3 blade CPP propeller at that time were priced at NOK 25,000, with a 20% direct order discount available. This assembly translates to a cost of USD $2,203, ex works, if making the same assumptions.

______________________________________

CPP Whole Shebang: USD $7,489 plus freight of around USD $350 and import brokerage of around USD $50, for a very approximate total of around USD $7,889 with shipping, but without taxes.

FPP: Fixed Pitch Propeller Equipment

The Twin Disc MG-5050, also suited to the needs of the Lugger 668-T, retails for USD $3,570. A "builder's" 10% discount is sometimes available, so let's use approximately USD $3,213.

A comparable stern gear "assembly" is offered by Vetus and includes shaft, bearing, stuffing box, and shaft tube. I don't have a current price from Vetus for this, but we might be able to assemble the pieces one by one, again assuming a 60mm shaft and 3 blade 660mm prop (around 26 inches), and taking the retail prices:

Coupling: Usually supplied with Gear

Shaft: Aquamet approx: USD $1,500

Machining on Shaft (Both Ends): approx: USD $500

Prop: 26" 3 blade Ni Br Al prop (comparable to the Sabb / Helseth
alloy): approx USD $1,900.

Bronze Sleeved Cutless Bearing: approx USD $200

Stuffing Box: Varies, so assume approximately USD $400

Bronze Stern Tube Materials: 5' x 3" OD: USD $180

Machining on Stern Tube: Approx USD $400

Flange Fabricating on Stern Tube: Approx USD $350

___________________________________________

Tail shaft "assembly" amounts to a total of around USD $5,500
Twin Disc MG-5050 Gear comes to around USD $3,213
___________________________________________

FPP Whole Shebang: USD $8,713 without any shipping or taxes. The FPP costs given here are using current quotes from the Seattle area, and using materials of equal quality to the Sabb / Helseth system.

A few random thoughts...

These figures have factored in the miscellaneous goodies, the machining and the fabricating required to create an "equivalent" system in terms quality, and in terms of the self enclosed type of shaft arrangement offered by Sabb / Helseth. Of course one could argue that a Manganese bronze prop with an ordinary stainless shaft in a non-self-enclosed shaft tube will be less costly, but then we would not be comparing "like for like" in terms of quality and components.

The upshot of the above is that if you figure a bit of inflation on the NOK prices given above, the overall cost of the two systems are very nearly equal. If there has not been much inflation in the Sabb / Helseth costs, then the CPP arrangement is actually LESS costly than an FPP installation.

One should note that there are several CPP arrangements available from other manufacturers. Hundested equipment is excellent for example. The "break point" that I ordinarily use between Sabb and Hundested is around 200 hp. Below 200 hp, and Sabb is usual the more economical choice. Above 200 hp, and Hundested will likely be the more appropriate choice. However, Sabb is adding a new CPP gear at the upper end of their line, so this dividing line will soon move upward a bit.

With the FPP system, once it is installed you have an unknown situation in terms of whether the pitch is actually correct for your vessel, and you may need to factor in the added cost of an entire
haulout and re-pitching ceremony.

These are the economics that drive my usual recommendations in favor of the CPP system. As a further benefit, the CPP system will be more efficient in use and much more adaptable to variable vessel loadings, weather, maneuvering, etc.

I have ordered parts and spares from Sabb for my own Sabb diesel. I have usually phoned in the order using a credit card, and the parts are shipped air freight, usually the same day. I have typically received parts within a few days. That's better service than I often get when I order parts from Seattle, which is less than 80 miles away...

These thoughts are not meant to deprecate the excellent FPP equipment available, but are rather an attempt to encourage an open mind when making this choice during the course of a new vessel design.

I do not subscribe to the TWL list, so any correspondence intended for me should be sent direct.

All the best,
Michael Kasten”

Regards;
Mike Schooley

[Willallison]

Thanks Mike - as I said before, makes you wonder why they aren't incorporated more often....perhaps, if they manage to break into the recreational market a little more, then they will be....

[Portager]

Tom;

You might find this link http://www.caracolyachts.com/new%20cat_new%20yorker.htm interesting reading. They explain why they selected controllable pitch propellers for the "New Yorker" Catamaran Trawler. In addition to the engine loading benefits at reduced speed, they also improve single engine performance, because you can feather the prop that isn't being used, and maneuverability because you can reverse thrust without throttling the engine back and shifting gears.

Will;

I do not understand the reason for the lack of CPP popularity either, although I believe there is only one manufacturer for the recreational market and they are very far away. It seams SABB is more successful in Europe so maybe they concentrate their marketing effort in their local market? It could also be that some boat builders/buyers are not as progressive as yours truly. I never meet advanced technology I didn't like.

Regards;
Mike Schooley

[Portager]

Tom;

I found a report on tank testing of a trimaran that I think is relevant to the monohulls versus catamaran discussion. The entire report can be found at http://www.theyachtreport.com/PROJEC...paper32000.pdf , but I think the abstract summarizes the relevant points very well. “This paper discusses the possible merits and disadvantages of a trimaran over a monohulls yacht. The powering performance and ship motion behaviour are evaluated for a modern 60 m monohull motor yacht and a trimaran with comparable displacement and installed power. Special emphasis is put on discomfort related to vertical and transverse accelerations. It is concluded that an increase in speed of 2 to 3 knots is possible for the trimaran. Comfort and workability on board a trimaran are superior over a monohull when sailing or at anchor in head seas. In quartering seas, the roll motions and transverse accelerations of this particular trimaran showed to be less tolerable than of the monohull. If these can be solved with special attention to the design of roll stabilising appendages, a trimaran can be a worthwhile option for owners who need a large deck area or who wish to stay onboard a longer than average period of the year.”

Obviously this report is based on much larger vessels than we were discussing and they are talking about a Trimaran instead of a Catamaran, but I believe the Catamaran, with its buoyancy further from the center of gravity plus the smaller size will only exacerbate the problems in quartering seas.

Regards;
Mike Schooley

[alanfujii]

tdamico

I know I'm late in getting into this discussion but I was searching the internet on this topic and found it interesting reading. I writing to see if you ever came to a conclusion on the type of boat you were seeking? I was also very interested in the Mirage Mfg's Navigator 37 and read the arguments of Mr. Codega. I found it interesting though the Mirage web site no longer has a link to this article, "The A/B Ratio Is Largely Meaningless By Lou Codega Naval Architect". I'm wondering whether this means they have backed off on the claim that this hull design was more than a coastal cruising type?

[tdamico]

This post is quite old. I can't say what Mirage's position is on the a/b ratio. I know that I am looking at only full displacement hulls based on my last 6 months of reasearch and also looking carefully at this ratio. I have ruled out the Mirage after visiting them at TrawlerFest.

[John Capuano]

I have enjoyed this discussion very much.Iam looking fof a boat along the same lines as tdamico.Several years ago I helped a friend bring a 55 footer to Seattle from Portland.The yacht was a Ocean Alaxander,a semi displacement hull.We caught an unusual summer storm,with waves 15 to 25 foot.It was impossible to run parallal with the coast.Best we could was zigzag.After 12 hours we started to hear strange sounds coming from the engine room every time we turned to port to zigzag out to sea.Turns out that the fuel tanks had no baffels to slow the fuel from sloshing side to side.We healed over so hard several times I thought we were going over.Now that Iam in the market for a boat of my own Iam reminded of that trip often.Proper fuel tank deisgn seems to be an often overlooked item.Any thoughts on this subject would be helpful. I have also posted a question under Powerboats/Dream Engines which could be helpful to tdamico and myself about prop and engine selection.