Thursday, July 29, 2010

Cooling Load Calculations for an 37' LNVT

Used Dometic's guidelines for sizing cooling load for a 37' LNVT. For a temperate climate need 22,000 Btus (1.8 tons) while a tropical climate requires 28,700 Btus (2.4 tons). Assuming a tropical climate, the load could be easily divided between two air conditioning units: 18,000 Btus (1.5 tons) for the pilothouse and stateroom; and, 12,000 Btus (1 ton) for the salon. At 250gph/12,000 Btus, need a 1" thru hull and a 750 gph raw water circulator.

ZoneSq. Ft.Temperate FactorTemperate BtusTropical FactorTropical Btus

The next question that needs to be answered is the CFM required in each space and from that the number and size of supply air ducts can be calculated.

Monday, July 26, 2010

The Big Engine Room Wrench

The LNVT wrench, mounted on the engine room's forward bulkhead, fits 3" and 3-1/2" nuts. The 3-1/2" fits the prop shaft's packing gland. The 3" fits the rudder shaft's packing gland. Several years ago Nellie's rudder packing started leaking badly. But then just as quickly it stopped. I believe the reason was due to water salinity—we'd gone from saltwater to fresh. The difference in buoyancy between salt and fresh water must be enough to move the water line from below the rudder shaft's packing gland to above it.

Saturday, July 10, 2010

Tug-For-Two #42 Cruising Blog

Finally was able to get a trial copy of Microsoft Publisher 2007 to read the Irvin's, Tug-for-Two (42), cruising blog. Moved the text over to a couple of Wiki pages: Will put the pictures in next. Long documents don't seem to work well as a web page.

Friday, July 9, 2010

Knock Off #66 Operation and Maintenance Manual

John Niccolls, Knock Off (66), gave me a rich text format of a MS Publisher document he's working on; an Operation and Maintenance (O&M) Manual for KO. I've converted this into an HTML document and posted it at: I'm hoping that this can act as a model for others that want to make O&M manuals for their tugs.

Thursday, July 8, 2010

Limber Holes

I've noticed on Nellie D. and Titan that any water which collects on the outside of the port, engine-mount bed, just sits there. There's no limber hole to allow the water to drain into the bilge.

Wednesday, July 7, 2010

The Bow Wave

I'd read that a bow wave moves aft as the hull accelerates. In fact, I believe it's a displacement hull's inability to get over the bow wave that results in hull speed. This 4th of July weekend while out on Knock Off I took the following series of pictures. No doubt the wave is moving aft.

4.7 knots at 1000 rpm
5.2 knots at 1200rpm
6.1 knots at 1400rpm
6.8 knots at 1600rpm
7.35 knots at 1800rpm

Tuesday, July 6, 2010

Adding a Bulwark Door

Bulwark Door Installation Lessons Learned

1. Install the door at the same time you're painting/repairing the bulwark.

2. Cutting the door out carefully will save a lot of finish work. The thin kerf of a sawzall blade creates the perfect spacing between the bulwark's caprail and the door's caprail.

3. After the door is cutout, finish the bulwark part of the job first. The finished bulwark can then be used to size and trim the door--just don't touch the door's teak caprail ;-).

4. Get hinges that don't have a lot of end play (i.e. axial movement between the leaves) or side play (the amount of movement of the leaves perpendicular to the pin). 'Loose' hinges will make your life miserable.

5. Hinge the door on the forward side and have it open inwards. Hinging it forward means you won't have to walk past it when boarding and going aft toward the companionway. Hinging it to open inwards keeps the door safe from docks and pilings.

6. Bevel cut (see picture below) the unhinged side. The door will fit tighter and look better.

7. Keep the fiberglass jam panel below the caprail. With the door closed the teak caprail should look continuous.

8. Put a strike plate or other support between the bottom of the door and the threshold. The strike plate supports the unhinged side of the closed door. Somebody, sooner or later, will walk on the door's caprail and without the strikeplate the hinges could be damaged.

9. Think about how best to finish-out the threshold. Big, expensive boats put in shiny stainless thresholds with the manufacturer's insignia on them. Lots of 'cool points' there. With a little forethought the same could be done here.

10. Choose a latch that that is both effective and doesn't stick out so much that it snags unsuspecting passers-by.

LNVTSide InstalledHow Door Opens
Lady (8)port sideopens inboard and towards bow
Moby (14)port sideopens by lifting up and out 
Titan (31)starboard sideopens inboard and towards bow
Neptune (35)starboard sideopens inboard and towards stern
Sea Turtle (40)starboard sideopens inboard and towards stern
Mocko Jumbie (49)port sideopens inboard and towards stern
Nellie D. (63)starboard sideopens inboard and towards stern
Fram (71)starboard sideopens inboard towards the bow
J. Edgar Moser (76)
starboard side
opens outboard and towards stern
* Update: Lil' Toot, starboard side, opens inwards towards the bow (added 2016).

Here's a link to pictures of many of the bukwark doors:,authkey:Gv1sRgCLWXyYeAxfWmPg

Monday, July 5, 2010

LNVT 37' Production by Month

Finally had enough of the hull numbers to put this graph together. Several things can be seen from it. Not many hulls were made in the last quarter of the year. According to Lani Hart this was because of the high humidity at that time of the year in Taiwan. A hull laid-up in a highly humid environment may suffer blistering. The order of the hulls is in no way chronological. Unfortunately, there's no way to tell from this chart when the interior work on the hull began.

Sunday, July 4, 2010

Knock Off #66's Roll Chocks

Got to experience Knock Off's (66) new roll chocks today. The Chesapeake was calm but we did get waked by some large boats. The chocks' damping effect can really be felt—there's a definite deceleration and the rolling period is longer.

Thursday, July 1, 2010

The following is the beginning of a future web page which will help folks sell their tugs. Need to get lessons learned from both buyers and sellers.

Selling your Tug: Lessons Learned

Naturally, keeping the tug in good condition will increase its selling price. However, knowing the competition may be just as important. Sellers often only know their own tug. Buyers, however, will most certainly look at multiple tugs. Only by researching the other tugs for sale on the market, to determine what shape they're in, what equipment they have, what their asking price is, etc., can the market value of ones own tug be determined. The bottom line is, if a tug isn't selling the price is too high. Put your tug in a location where it'll get lots of traffic, both walk- and drive-by. Think about co-locating your tug with another tug that's for sale. If selling through a broker, get an experienced one. One familiar with LNVTs and comfortable selling classic boats. The site averages 3,000 visitors a month and . Keep your tugs photos and data complete and current. Done right, it'll help attract buyers and keep 'tire kickers' at bay. Take good pictures of the tug. Here's an example for some interior shots. Use a wide angle lens.