repower for 1969 46 MY

The “quotes” were merely to emphasize the irony of thinking our Roamer could get up on plane. Even at WOT she never seemed to drop down to being on plane.
To remark further on her fuel usage:
The best fuel economy we saw was made traveling down-river on the Mississippi.
While we had made c12.5 mph at 1500 to 1600 rpm on the lakes and the Illinois River System, she picked up to c17.5 mph for the same rpm settings on much of the Mississippi. We covered 296 miles from Grafton, IL to Golconda, IL on 310 gallons of diesel (78 miles of that was going up the Ohio River). Still, that was 0.95 mpg, just 79.5 yards short of a mile. Going up the Ohio our fuel usage averaged out to more or less 4/5ths of a mile per gallon for the other 903 miles to Pittsburgh. If you subtract the 78 miles up the Ohio at 4/5ths mpg, then we were getting on the order of 1.0287 mpg down the Mississippi or 5431.5 feet per gallon (more than 1 mpg yet less than 1 nmpg.) Still, that's just adding the flow of the river. Otherwise we never came close to a mile per gallon when refueling after any leg of the trip. When all is said and done it sounds as if still water boating on our Roamer comes to something nearer to 9/10ths mpg, if you could find such a place. Ain't it fun?
When I finally can download the data from our trip record on the GPS, perhaps all this will come into sharper focus. If anything is wildly different from my calculations; I’ll pass it on.
In the mean time all that is based solely on our running log entries.

The first time I saw a PT Boat was for real, it was spring of 1943, and we encountered a PT boat roaring up the Elizabeth River towards the Norfolk Navy Yard in Portsmouth, VA. It had a huge open shark’s mouth painted around the front, was really plowing up the water, and was throwing off a wake four or five feet deep. I almost wished she had been up on plane. My Grandfather passed her port-to-port and we dropped over that first wave then nosed up through the second one in our 28-foot cruiser. I don’t know how fast she was moving, but I barely had time to hurry through the cabin and secure the two front windows before we hit her wake.

I don’t have the feeling that our 46' Roamer was designed with being on plane in mind… but then what do I know, I’m a high school drop-out anyway!
The following slingshots were made shortly before we got underway when we had her lifted to clean the bottom and install a new depth sounder/fish finder:

Definition of planing speed

Here I go again (remember, I'm the long winded guy). I just had to chime in here regarding this "are we planing or not" conversation.

I was taught the simple test for being "on plane" is when the bow comes back down. If it just rises, you are plowing = least efficient use of fuel. Then by definitiuon that I've read over the years: planing = "the speed at which a boat climbs onto it's bow wave and leaves it's stern wave behind". This concurs with the the beer drinking conversation "when the water leaves the transom cleanly" and I believe that is when the bow drops over that 'hump'. The idea that "to lift the boat" defines planing is not the whole story.

So I scoured Dave Gerr's book 'The Nature of Boats' and found some interesting calculations. The beginning point of planing can be calculated using the waterline length. The longer the boat, the higher the speed needed to plane. Multiply the sq root of the LWL by a 'speed to length' ratio factor to get the speed at which you 'start planing'. Those factors are 2.5 - 2.7 for flat bottomed, 2.7 - 3.0 for shallow V to modified V, and 2.9 -3.1 for deep V and Heavy V bottom cruisers.

Presuming our Roamer 46 is at least a mod V and at worst a heavy cruiser, let's use 2.8 x 6.4 (guessing LWL= 41) = 17.9 knots to begin 'to plane' (19.84kt if it's a heavy cruiser). There is another chart to determine the HP needed to do that based on power to weight ratio. But he warns against using the manufacturer's advertised weight

This is a very interesting book written by the naval architect who heads the Westlawn Institute of Marine Technology (AYBC's training school). I've met him a couple times and he really tries to make all this techinical stuff interesting. The book is worth having on your shelf.

q240z, in answer to your question about weight, after having waited for three weeks while watching green "boat mechanics and electricians" scratching their heads as they wondered "what to do" at $60. per, my primary interest was getting underway!
Sorry, I can't help with that one.
I'll measure the LWL tomorrow, but I don't think it is more than three feet less than the overall.
However, in the meantime, here's a site with some interesting formulas:
http://powerboat.about.com/od/hulls/a/displacement.htm

quoting http://www.olsenmarine.com/info.htm -

"AN INTRODUCTION TO THE HUCKINS GURNET 36
by Olsen Marine



First and foremost, the Gurnet is light, seaworthy, fast and efficient Twin engines provide maneuverability, safety and high speed. Located at the transom, the engines are quiet, easily accessed, yet out of the way. With standard power, the boat begins to plane at 8 knots, has fully planing cruising speeds from twelve knots to twenty-six, and a top speed of about twenty-eight knots.

The hull has a warped Quadraconic bottom providing a soft ride over a wide range of speeds, with better stability at displacement speeds and at rest than a deep v-bottom. Full bow sections provide superb buoyancy, with plenty of room below decks. The hull has good freeboard, allowing room and security for passengers. Carefully designed chines minimize spray. A well-designed superstructure protects the operator and passengers from the elements, yet affords excellent visibility. Since the boat planes easily, there is little change in running angle as speed increases resulting in no visibility problems. Trim tabs are not necessary. Because the boat is designed and built to be light, relatively little power is needed to achieve a given speed making the boat economical to run."

Assuming even the best number put forth by Gerr and a 34' LWL, that boat shouldn't even approach planing until 14.5kts. And yet it's at least partially planing at 8, and fully planing cruising speed at 12! Fabrications? Or are all Huckins advocates insane?

It's probably wasted keystrokes to even get into the discussion further because it really takes an trip aboard one to dispel the doubts of the naysayers and prove that it's more than a crackpot claim, so I'll stop now.

Hi,

No doubt this will get a bite or two.

If ya stick to large displacement moderate speed diesels and the vessels they are suited to the foregoing thread is a non starter.

(Mods - If I have tipped a few pink gins during the keyboard frenzy please feel free to delete my possible inflammatory comments) We do not after all want those wooden boats to spontaneously combust at their Owners/Admirers reaction.

Lwl

q240z, I measured the LWL today and it seems to be 42'. Then I returned home and used some of the formulas offered in this forum and here are the results:
46' Roamer
LWL = 42 feet
Sq root = 6.4807406984

Maximum Hull speed:
8.6841925359 Knots = 9.9868214163 MPH

Speed necessary to plane:
Knots MPH
X2.8 = 18.1460739555 = 20.8679850488
X2.9 = 18.7941480254 = 21.6132702292
X3.0 = 19.4422220952 = 22.3585554095
X3.1 = 20.0902961651 = 23.1038405899

Frankly speaking, I'm of the same mind as artwork.
It doesn't feel like planing until that final drop into position.
Even proceeding down river with 1.5 mph river flow helping to boost speed it
wasn't enough to accomplish the drop.
While the trim tabs lowered the bow enough to see well, I always felt that they were just holding her "almost there" and that was it.
During the sea trial in 2005 the GPS was showing her top speed as 20 mph on the basically still waters of Lake St Clair.

q240z there is a guy on ebay parting a Roamer with a pair of detroits. This ad is for the instrument panel assembly and does not indicate that the engines are for sale or already sold but it's a lead.
http://cgi.ebay.com/ebaymotors/chri...003QQitemZ130190099854QQrdZ1QQsspagenameZWDVW