Phil, I guess it all depends on what you mean by having an "8 knot hull". We don't, as a matter of course, cruise at hull speed. Our hull has a theoretical hull speed of 7.8 ktrs (1.34 X the square root of our 34' W/L). We normally cruise at about 6.5 kts. (a factor of only 1.1) and enjoy great fuel economy but are happy to have the extra HP available when we are trying to make the one-an-hour bridge opening at Sunset Beach. If you have just a little adverse wind and a small unfavorable current and it can turn into a really long day! Regards, Randy Pickelmann MORNING STAR lying in Clearwater, FL www.morningstar.talkspot.com ----- Original Message ---- From: Phil de l'Etoile <pdeli3@gmail.com> To: Randy Pickelmann <rwp_48@yahoo.com> Cc: trawlers-and-trawlering@lists.samurai.com; FloridaKeyz@aol.com Sent: Tuesday, July 15, 2008 9:58:34 AM Subject: Re: T&T: Hull speed theoreticall What I'm not understanding on this subject about additional power above hull speed requirements is the current considerations. If I have an 8 knot hull requiring 50 hp, and if 8 kn is truly the upper limit, what good is 100hp if I'm going uphill in an 8 kn current? Or any current for that matter! Wind is a different story I assume, because, although there may be a practical limit, there is no theoretical hull speed as respects wind. So basically isn't it just the wind that we expect to overcome here with additional power? I know I must be missig something, but what? Phil On 7/15/08, Randy Pickelmann <rwp_48@yahoo.com> wrote: > Cap't Sterling, > When Krogen first built the Manatee they installed a 50 HP Perkins. That > only > lasted a few hulls and they switched up to a 90 HP Volvo. Before they were > done they used a 100 HP and 110 HP Volvo although I suspect that these were > model changes in the motor as opposed to changing expressly to get more HP. > Likewise, Great Harbour used twin 39 HP Yanmars in their first 37 but > switched > to the 54 HP. I think that the "theoretical" HP requirements are fine...if > you are in an office. But when you are bucking the tide, trying to make a > bridge or the wind is on the nose and will be all day, the extra HP is > generally a good trade-off. > Regards, > Randy Pickelmann > MORNING STAR > lying in Clearwater, FL > www.morningstar.talkspot.com > _______________________________________________ > http://lists.samurai.com/mailman/listinfo/trawlers-and-trawlering > > To unsubscribe or modify your subscription options (get password, change > email address, etc) go to: > http://lists.samurai.com/mailman/options/trawlers-and-trawlering > > Trawlers & Trawlering and T&T are trademarks of Water World > Productions. Unauthorized use is prohibited.

Randy, To perhaps be more clear, what I was trying to do is take the wind out of the equation and use hull speed in order to somewhat purify the analysis. In other words I'm saying that it seems to me that the speed of the hull is limited to just that whether it is made up of no current and 8 kn SOG, or 5 kn of current and 3 kn SOG. Even going with the current I'd still have the 5 kn current plus the 8 kn hull speed for a total of 13 kn SOG. In all cases the hull speed is the same - just the SOG varies. So if you can attain hull speed at say 50% throttle, what would you ever use the top 50% for? That's what I was trying to get at - make sense? I'm not looking to push to hull speed, but rather I'm trying to understand why I would ever need more than let's say 125% of the otherwise required HP. More personally, on my 37' displacement boat I can get to 7.0-7.5 kn at about 17-1800 rpm. WOT is around 24-2500 rpm. I believe that I may only need 50 hp to attain hull speed, but I happen have a 150 hp engine. I must also admit that I am seldom, if ever, not involved with current, so my measurements here may be a little off. Nonetheless they seem fairly reasonable. In the absence of any flawed reasoning here, it seems to me that I may only need the extra power to fight the wind. What am I missing? Phil On Tue, Jul 15, 2008 at 6:42 PM, Randy Pickelmann <rwp_48@yahoo.com> wrote: > Phil, > > I guess it all depends on what you mean by having an "8 knot hull". We > don't, as a matter of course, cruise at hull speed. Our hull has a > theoretical hull speed of 7.8 ktrs (1.34 X the square root of our 34' W/L). > We normally cruise at about 6.5 kts. (a factor of only 1.1) and enjoy great > fuel economy but are happy to have the extra HP available when we are trying > to make the one-an-hour bridge opening at Sunset Beach. If you have just a > little adverse wind and a small unfavorable current and it can turn into a > really long day! > > Regards, > > Randy Pickelmann > > MORNING STAR > > lying in Clearwater, FL > > www.morningstar.talkspot.com > > > > ----- Original Message ---- > From: Phil de l'Etoile <pdeli3@gmail.com> > To: Randy Pickelmann <rwp_48@yahoo.com> > Cc: trawlers-and-trawlering@lists.samurai.com; FloridaKeyz@aol.com > Sent: Tuesday, July 15, 2008 9:58:34 AM > Subject: Re: T&T: Hull speed theoreticall > > What I'm not understanding on this subject about additional power > above hull speed requirements is the current considerations. > > If I have an 8 knot hull requiring 50 hp, and if 8 kn is truly the > upper limit, what good is 100hp if I'm going uphill in an 8 kn > current? Or any current for that matter! > > Wind is a different story I assume, because, although there may be a > practical limit, there is no theoretical hull speed as respects wind. > > So basically isn't it just the wind that we expect to overcome here > with additional power? > > I know I must be missig something, but what? > > Phil > > On 7/15/08, Randy Pickelmann <rwp_48@yahoo.com> wrote: >> Cap't Sterling, >> When Krogen first built the Manatee they installed a 50 HP Perkins. That >> only >> lasted a few hulls and they switched up to a 90 HP Volvo. Before they >> were >> done they used a 100 HP and 110 HP Volvo although I suspect that these >> were >> model changes in the motor as opposed to changing expressly to get more >> HP. >> Likewise, Great Harbour used twin 39 HP Yanmars in their first 37 but >> switched >> to the 54 HP. I think that the "theoretical" HP requirements are >> fine...if >> you are in an office. But when you are bucking the tide, trying to make a >> bridge or the wind is on the nose and will be all day, the extra HP is >> generally a good trade-off. >> Regards, >> Randy Pickelmann >> MORNING STAR >> lying in Clearwater, FL >> www.morningstar.talkspot.com >> _______________________________________________ >> http://lists.samurai.com/mailman/listinfo/trawlers-and-trawlering >> >> To unsubscribe or modify your subscription options (get password, change >> email address, etc) go to: >> http://lists.samurai.com/mailman/options/trawlers-and-trawlering >> >> Trawlers & Trawlering and T&T are trademarks of Water World >> Productions. Unauthorized use is prohibited.

My research indicates that fuel economy may double by decreasing speed to about 0.8 x the square root of the water line length, from 1.1. Mike _____________________________________ Capt. Mike Maurice Tigard Oregon(Near Portland)

Phil, I understand the mental exercise that doing. You are absolutely correct in that your speed through the water is limited and current affects that and there is nothing you can do about it. If you put a Pratt & Whitney jet engine in a Krogen Manatee you aren't going to go much more than hull speed. As you increase the power you burn more fuel and dig yourself a hole in the water. However, in the real world we have to deal with current and wind and frequently the waves that combination causes too. In those cases, I am glad to be able to increase the power a bit to maintain speed instead of loosing it. I know that the 120 HP Ford Lehman was a popular engine for GB, Marine Trader and a number of other Taiwanese-built trawlers in the '70's and '80's. I don't know if it was because they were available and well priced or because the marketing folks were driving engine selection. Can you hear it?..."Boss, their boat has a 120 HP engine and ours only has an 80! We're gonn'a get killed at the boatshow!" Regards, Randy Pickelmann MORNING STAR lying in Clearwater, FL www.morningstar.talkspot.com ----- Original Message ----- From: "Phil de l'Etoile" <pdeli3@gmail.com> To: "Randy Pickelmann" <rwp_48@yahoo.com> Cc: <trawlers-and-trawlering@lists.samurai.com> Sent: Wednesday, July 16, 2008 12:22 AM Subject: Re: T&T: Hull speed theoretical > Randy, > > To perhaps be more clear, what I was trying to do is take the wind out > of the equation and use hull speed in order to somewhat purify the > analysis. In other words I'm saying that it seems to me that the > speed of the hull is limited to just that whether it is made up of no > current and 8 kn SOG, or 5 kn of current and 3 kn SOG. Even going > with the current I'd still have the 5 kn current plus the 8 kn hull > speed for a total of 13 kn SOG. In all cases the hull speed is the > same - just the SOG varies. > > So if you can attain hull speed at say 50% throttle, what would you > ever use the top 50% for? That's what I was trying to get at - make > sense? > > I'm not looking to push to hull speed, but rather I'm trying to > understand why I would ever need more than let's say 125% of the > otherwise required HP. > > More personally, on my 37' displacement boat I can get to 7.0-7.5 kn > at about 17-1800 rpm. WOT is around 24-2500 rpm. I believe that I > may only need 50 hp to attain hull speed, but I happen have a 150 hp > engine. > > I must also admit that I am seldom, if ever, not involved with > current, so my measurements here may be a little off. Nonetheless > they seem fairly reasonable. > > In the absence of any flawed reasoning here, it seems to me that I may > only need the extra power to fight the wind. > > What am I missing? > > Phil > > > > On Tue, Jul 15, 2008 at 6:42 PM, Randy Pickelmann <rwp_48@yahoo.com> > wrote: >> Phil, >> >> I guess it all depends on what you mean by having an "8 knot hull". We >> don't, as a matter of course, cruise at hull speed. Our hull has a >> theoretical hull speed of 7.8 ktrs (1.34 X the square root of our 34' >> W/L). >> We normally cruise at about 6.5 kts. (a factor of only 1.1) and enjoy >> great >> fuel economy but are happy to have the extra HP available when we are >> trying >> to make the one-an-hour bridge opening at Sunset Beach. If you have just >> a >> little adverse wind and a small unfavorable current and it can turn into >> a >> really long day! >> >> Regards, >> >> Randy Pickelmann >> >> MORNING STAR >> >> lying in Clearwater, FL >> >> www.morningstar.talkspot.com >> >> >> >> ----- Original Message ---- >> From: Phil de l'Etoile <pdeli3@gmail.com> >> To: Randy Pickelmann <rwp_48@yahoo.com> >> Cc: trawlers-and-trawlering@lists.samurai.com; FloridaKeyz@aol.com >> Sent: Tuesday, July 15, 2008 9:58:34 AM >> Subject: Re: T&T: Hull speed theoreticall >> >> What I'm not understanding on this subject about additional power >> above hull speed requirements is the current considerations. >> >> If I have an 8 knot hull requiring 50 hp, and if 8 kn is truly the >> upper limit, what good is 100hp if I'm going uphill in an 8 kn >> current? Or any current for that matter! >> >> Wind is a different story I assume, because, although there may be a >> practical limit, there is no theoretical hull speed as respects wind. >> >> So basically isn't it just the wind that we expect to overcome here >> with additional power? >> >> I know I must be missig something, but what? >> >> Phil >> >> On 7/15/08, Randy Pickelmann <rwp_48@yahoo.com> wrote: >>> Cap't Sterling, >>> When Krogen first built the Manatee they installed a 50 HP Perkins. >>> That >>> only >>> lasted a few hulls and they switched up to a 90 HP Volvo. Before they >>> were >>> done they used a 100 HP and 110 HP Volvo although I suspect that these >>> were >>> model changes in the motor as opposed to changing expressly to get more >>> HP. >>> Likewise, Great Harbour used twin 39 HP Yanmars in their first 37 but >>> switched >>> to the 54 HP. I think that the "theoretical" HP requirements are >>> fine...if >>> you are in an office. But when you are bucking the tide, trying to make >>> a >>> bridge or the wind is on the nose and will be all day, the extra HP is >>> generally a good trade-off. >>> Regards, >>> Randy Pickelmann >>> MORNING STAR >>> lying in Clearwater, FL >>> www.morningstar.talkspot.com >>> _______________________________________________ >>> http://lists.samurai.com/mailman/listinfo/trawlers-and-trawlering >>> >>> To unsubscribe or modify your subscription options (get password, change >>> email address, etc) go to: >>> http://lists.samurai.com/mailman/options/trawlers-and-trawlering >>> >>> Trawlers & Trawlering and T&T are trademarks of Water World >>> Productions. Unauthorized use is prohibited.

You might need it to tow something or somebody. You might need it to get yourself ungrounded. You might need it to get someone else ungrounded. You might need it to haul around all the extra stuff you and your spouse pile onto the boat. You might need it to get past all the friction caused by all the crap that grows on the bottom of your boat that the theoretical formula does not account for. Your boat gets a little slower every minute it is sitting in the water. You might need it to maneuver in tight quarters with heavy wind or current(this is where current comes into play regardless of hullspeed...you want the boat to change directions right NOW!!!). You might need it to get your boat to hullspeed because the hull shape is not what this magical equation assumes. Phil, this is just some stuff I thought of right of hand. Maybe someone else can think of some others. My main point here is that we live in reality and not in theory. The boat I own right now is semi-planing and has the power to plane so it doesn't count in this discussion. My previous boat was a displacement cruiser. 1800rpm power put it right at hullspeed and that is where I cruised it. That yielded about 6.7kts thru the water(small boat). As time went on(months or even years), that speed would deteriorate so I could either accept the slowdown or push the power up a little bit(or haul the boat and clean it and/or get new paint). WIth your theoretical boat/engine, you can't really push the power up because you start straining the engine and siginificantly increasing fuel burn. Are you willing to accept the slow degradation of speed mainly due to drag and weight? Are you willing to cruise it at 80 or 85% power as your perfect theoretical boat becomes not so perfect in reality? Another thing to consider for power settings and calculations is that there is a power CURVE and not a power LINE! In other words, the power that your engine produces is not linear....especailly if the engine is turbocharged. 1800rpm/2600rpm equals 70% if we assume linear power. My only point here is unless you have the power curves/charts given by the manufacturer, your estimation of percentage of power is a very rough guess. My current engine produces 190hp at 3100rpms and 240hp at 3300rpms. That is 25hp per 100rpms. If that was a linear relationship(25hp per 100rpms), my little Yanmar would be a 750hp engine at 3000rpms....you get the picture. Trawler on, John Please visit www.trawlerforum.com

<< I know that the 120 HP Ford Lehman was a popular engine... I don't know if it was because they were available and well priced or because the marketing folks were driving engine selection. >> The latter. Lehman also had an 80 hp 4-cylinder available, but they were way less popular than the 120 hp 6-cyl. Several Taiwanese trawler models were offered with either a single 120 Lehman, or with 2-120 Lehmans. Surely the twin could have been better powered with the 4-cyl Lehmans. Mark Richter, m/v Winnie the Pooh

<<My research indicates that fuel economy may double by decreasing speed to about 0.8 x the square root of the water line length, from 1.1.>> Mike, I believe your statement, but how many trawlers have engines small enough to be happy traveling at such low speeds? For Pooh (41 ft LWL), those speeds translate to 7.0 kts, running at 1600 rpm, and 5.1 kts, running at 1150. My engine vibrates more at speeds below 1300-1400 rpm, and Pooh (80 hp and 33,000 lbs) is probably the second-lowest-powered trawler on the list. How can similar-sized or even smaller trawlers powered with 240 hp going to manage to slow to these economical speeds? It seems that many here on the list don't believe that even 150% of the power needed to achieve hull speed is enough for their trawler. No wonder nearly all our boats are massively overpowered. A couple of years ago with fuel at $1.50, the cost of carrying around all this extra power was manageable. But we've now entered an era where the ultimate cost of too much power is to park the boat. Mark Richter, m/v Winnie the Pooh lying Albion, NY on the Erie Canal (most of which is a no-wake zone)

I had a 34 CHB with twin 80's. I think I only really needed one engine though (except when docking since that was before I learned to park a single.) Phil On Wed, Jul 16, 2008 at 1:10 PM, Mark Richter <richter-pooh@rocketmail.com> wrote: > << I know that the 120 HP Ford Lehman was a popular engine... I don't know > if it was because they were available and well priced or because the > marketing folks were driving engine selection. >> > > The latter. Lehman also had an 80 hp 4-cylinder available, but they were > way less popular than the 120 hp 6-cyl. Several Taiwanese trawler models > were offered with either a single 120 Lehman, or with 2-120 Lehmans. Surely > the twin could have been better powered with the 4-cyl Lehmans. > > Mark Richter, m/v Winnie the Pooh > _______________________________________________

I didn't mean to imply that boats have engines that would be happy at 0.8, just that such speeds are conducive to great fuel economy. By the way the BC ferries are about 500 feet long for a square root of about 22 and are running about 19 knots, which is about 0.85. I assume that this is intentional. Mike _____________________________________ Capt. Mike Maurice Tigard Oregon(Near Portland)