Sizing props

Howdy; Our Cal 39 has a brand-new Yanmar 3jh3e engine, which is rated for 36 HP continuous at 3650 RPM. Wide-open throttle is rated at 4000 RPM, which according to the specs should generate 40 HP. Diesel mechanic said the RPM gauge is calibrated correctly and the engine is running fine, so we're fairly confident that we're getting the rated HP to the shaft. Hull speed for this boat, based on a LWL of 32' 1" from the sales specs, should be around 7.6 knots. When sailing In 10-12 knots on a reach, this boat bombs along at over 8 knots, so I know its an easily-driven hull shape, more than capable of reaching hull speed. We have a reversing prop, don't know the type, a picture is attached. Have not measured the prop, but estimate that the 3 blades are about 5 or 6 inches from base to tip, and about 4 to 5 inches across at widest point. Hard to estimate pitch. The reversing mechanism works well. If anyone recognizes the type of prop, would appreciate some info on it. All of the above is for background info. Now: on our boat, 3600 RPM in flat water and a clean hull gets us up to about 6.5 knots. Haven't really pushed it to WOT for very long, but it doesn't add much to the speed, maybe goes up to around 7 knots at best. We're suspecting that the prop is not pitched correctly or is undersized, or both. We'd like it to be more efficient, not because we want to water-ski, but for motoring to weather offshore when the seas are rough. OTOH, maybe the engine is too small? Would appreciate any input mainly from other cal 39 owners who may have done adjustments on their props or changed their HP during repowers, or who can compare their top cruising speeds to ours. At this point it's a minor issue but we'd like to know what we're facing if we decide to work on it. Thanks! bw Cal 39-2 #003 "Sea Star" SF Bay

--- In Ca… [at] yahoogroups.com, "Bob Walden" <bob@...> wrote: > > Howdy; > > Our Cal 39 has a brand-new Yanmar 3jh3e engine, which is rated for 36 HP continuous at 3650 RPM. Wide-open throttle is rated at 4000 RPM, which according to the specs should generate 40 HP. That looks like a two blade MaxProp and it looks small to me. Here is their site: http://www.max-prop.com/2-blade-classic.html The sizing info is there. Mike Kennedy Conquest Cal 40 #96

well, it's actually a 3-bladed prop--see this pic. From: "mtkennedy1" <mt… [at] cox.net> To: <Ca… [at] yahoogroups.com> Sent: Saturday, February 10, 2007 6:31 PM Subject: [Cal_Boats] Re: Sizing props > --- In Ca… [at] yahoogroups.com, "Bob Walden" <bob@...> wrote: >> >> Howdy; >> >> Our Cal 39 has a brand-new Yanmar 3jh3e engine, which is rated for 36 HP >> continuous at > 3650 RPM. Wide-open throttle is rated at 4000 RPM, which according to the > specs should > generate 40 HP. > > > That looks like a two blade MaxProp and it looks small to me. > > Here is their site: > > http://www.max-prop.com/2-blade-classic.html > > The sizing info is there. > > Mike Kennedy > Conquest Cal 40 #96 > > > > > Yahoo! Groups Links > > > > >

--- In Ca… [at] yahoogroups.com, "Bob Walden" <bob@...> wrote: > > well, it's actually a 3-bladed prop--see this pic. Three blade MaxProp. Same difference. Mike Kennedy Conquest Cal 40 # 96 > > ----- Original Message ----- > From: "mtkennedy1" <mtkennedy1@...> > To: <Ca… [at] yahoogroups.com> > Sent: Saturday, February 10, 2007 6:31 PM > Subject: [Cal_Boats] Re: Sizing props > > > > --- In Ca… [at] yahoogroups.com, "Bob Walden" <bob@> wrote: > >> > >> Howdy; > >> > >> Our Cal 39 has a brand-new Yanmar 3jh3e engine, which is rated for 36 HP > >> continuous at > > 3650 RPM. Wide-open throttle is rated at 4000 RPM, which according to the > > specs should > > generate 40 HP. > > > > > > That looks like a two blade MaxProp and it looks small to me. > > > > Here is their site: > > > > http://www.max-prop.com/2-blade-classic.html > > > > The sizing info is there. > > > > Mike Kennedy > > Conquest Cal 40 #96 > > > > > > > > > > Yahoo! Groups Links > > > > > > > > > > >

thanks Mike. Didn't look like the pics on maxprop's website, I never would have guessed. From: "mtkennedy1" <mt… [at] cox.net> To: <Ca… [at] yahoogroups.com> Sent: Saturday, February 10, 2007 8:38 PM Subject: [Cal_Boats] Re: Sizing props > --- In Ca… [at] yahoogroups.com, "Bob Walden" <bob@...> wrote: >> >> well, it's actually a 3-bladed prop--see this pic. > > Three blade MaxProp. Same difference. > > Mike Kennedy > Conquest Cal 40 # 96 > >> >> ----- Original Message ----- >> From: "mtkennedy1" <mtkennedy1@...> >> To: <Ca… [at] yahoogroups.com> >> Sent: Saturday, February 10, 2007 6:31 PM >> Subject: [Cal_Boats] Re: Sizing props >> >> >> > --- In Ca… [at] yahoogroups.com, "Bob Walden" <bob@> wrote: >> >> >> >> Howdy; >> >> >> >> Our Cal 39 has a brand-new Yanmar 3jh3e engine, which is rated for 36 >> >> HP >> >> continuous at >> > 3650 RPM. Wide-open throttle is rated at 4000 RPM, which according to >> > the >> > specs should >> > generate 40 HP. >> > >> > >> > That looks like a two blade MaxProp and it looks small to me. >> > >> > Here is their site: >> > >> > http://www.max-prop.com/2-blade-classic.html >> > >> > The sizing info is there. >> > >> > Mike Kennedy >> > Conquest Cal 40 #96 >> > >> > >> > >> > >> > Yahoo! Groups Links >> > >> > >> > >> > >> > >> > > > > > > Yahoo! Groups Links > > > > >

Bob, in the picture, are you sure that isn't the third thoracic vertebra from a T-Rex? : - ] Cheers Charlie From: Ca… [at] yahoogroups.com [mailto:Ca… [at] yahoogroups.com] On Behalf Of Bob Walden Sent: Saturday, February 10, 2007 9:53 PM To: Ca… [at] yahoogroups.com Subject: Re: [Cal_Boats] Re: Sizing props well, it's actually a 3-bladed prop--see this pic. From: "mtkennedy1" <mt… [at] cox.net> To: <Ca… [at] yahoogroups.com> Sent: Saturday, February 10, 2007 6:31 PM Subject: [Cal_Boats] Re: Sizing props > --- In Ca… [at] yahoogroups.com, "Bob Walden" <bob@...> wrote: >> >> Howdy; >> >> Our Cal 39 has a brand-new Yanmar 3jh3e engine, which is rated for 36 HP >> continuous at > 3650 RPM. Wide-open throttle is rated at 4000 RPM, which according to the > specs should > generate 40 HP. > > > That looks like a two blade MaxProp and it looks small to me. > > Here is their site: > > http://www.max-prop.com/2-blade-classic.html > > The sizing info is there. > > Mike Kennedy > Conquest Cal 40 #96 > > > > > Yahoo! Groups Links > > > > > Yahoo! Groups Links

Ah, that explains it. Must be a DinoProp. From: "Husar, Charlie" <hu… [at] bah.com> To: <Ca… [at] yahoogroups.com> Sent: Sunday, February 11, 2007 3:21 AM Subject: RE: [Cal_Boats] Re: Sizing props > Bob, in the picture, are you sure that isn't the third thoracic vertebra > from a T-Rex? : - ] > > Cheers > Charlie > > -----Original Message----- > From: Ca… [at] yahoogroups.com [mailto:Ca… [at] yahoogroups.com] On > Behalf Of Bob Walden > Sent: Saturday, February 10, 2007 9:53 PM > To: Ca… [at] yahoogroups.com > Subject: Re: [Cal_Boats] Re: Sizing props > > well, it's actually a 3-bladed prop--see this pic. > > ----- Original Message ----- > From: "mtkennedy1" <mt… [at] cox.net> > To: <Ca… [at] yahoogroups.com> > Sent: Saturday, February 10, 2007 6:31 PM > Subject: [Cal_Boats] Re: Sizing props > > >> --- In Ca… [at] yahoogroups.com, "Bob Walden" <bob@...> wrote: >>> >>> Howdy; >>> >>> Our Cal 39 has a brand-new Yanmar 3jh3e engine, which is rated for 36 > HP >>> continuous at >> 3650 RPM. Wide-open throttle is rated at 4000 RPM, which according to > the >> specs should >> generate 40 HP. >> >> >> That looks like a two blade MaxProp and it looks small to me. >> >> Here is their site: >> >> http://www.max-prop.com/2-blade-classic.html >> >> The sizing info is there. >> >> Mike Kennedy >> Conquest Cal 40 #96 >> >> >> >> >> Yahoo! Groups Links >> >> >> >> >> > > > > Yahoo! Groups Links > > > > > > > Yahoo! Groups Links > > > > >

--- In Ca… [at] yahoogroups.com, "Bob Walden" <bob@...> wrote: > > thanks Mike. Didn't look like the pics on maxprop's website, I never would > have guessed. > > ----- Original Message ----- > From: "mtkennedy1" <mtkennedy1@...> > To: <Ca… [at] yahoogroups.com> > Sent: Saturday, February 10, 2007 8:38 PM > Subject: [Cal_Boats] Re: Sizing props > > > > --- In Ca… [at] yahoogroups.com, "Bob Walden" <bob@> wrote: > >> > >> well, it's actually a 3-bladed prop--see this pic. > > > > Three blade MaxProp. Same difference. I could be wrong about the brand. Maybe there are lookalikes, as there are for Martecs. Still, the sizing rules should apply. Have you cleaned off the prop and looked for any ID ? I had a prop that I thought was a Martec but the Martec people pointed out it was an imitation made by Michigan Wheel. Mike Kennedy Conquest Cal 40 # 96

hmmm. no, we haven't cleaned it up much, but when it was out of the water during the survey we looked it over pretty good and did some scraping looking for markings, didn't find any. I guess next haulout we'll have to spend more time cleaning it and taking pics. From: "mtkennedy1" <mt… [at] cox.net> To: <Ca… [at] yahoogroups.com> Sent: Sunday, February 11, 2007 7:49 AM Subject: [Cal_Boats] Re: Sizing props > --- In Ca… [at] yahoogroups.com, "Bob Walden" <bob@...> wrote: >> >> thanks Mike. Didn't look like the pics on maxprop's website, I never >> would >> have guessed. >> >> ----- Original Message ----- >> From: "mtkennedy1" <mtkennedy1@...> >> To: <Ca… [at] yahoogroups.com> >> Sent: Saturday, February 10, 2007 8:38 PM >> Subject: [Cal_Boats] Re: Sizing props >> >> >> > --- In Ca… [at] yahoogroups.com, "Bob Walden" <bob@> wrote: >> >> >> >> well, it's actually a 3-bladed prop--see this pic. >> > >> > Three blade MaxProp. Same difference. > > I could be wrong about the brand. Maybe there are lookalikes, as there are > for Martecs. > Still, the sizing rules should apply. Have you cleaned off the prop and > looked for any ID ? I > had a prop that I thought was a Martec but the Martec people pointed out > it was an > imitation made by Michigan Wheel. > > Mike Kennedy > Conquest Cal 40 # 96 > > > > > > > Yahoo! Groups Links > > > > >

FYI, the Feb. issue of Practical Sailor has an article (The Cruiser's Drivetrain) that speaks well of the Kiwi Feather Prop. This is a 3-bladed prop where each blade feathers by water pressure independently of the others. Cost = about $1250 in the US. See www.kiwiprops.co.nz <http://www.kiwiprops.co.nz/> . Harleigh Ewell Cal 31 From: Ca… [at] yahoogroups.com [mailto:Ca… [at] yahoogroups.com] On Behalf Of Bob Walden Sent: Saturday, February 10, 2007 9:53 PM To: Ca… [at] yahoogroups.com Subject: Re: [Cal_Boats] Re: Sizing props well, it's actually a 3-bladed prop--see this pic.

Bob, When we bought our Cal 39 six years ago, it had a 2-blade folding prop that didn't allow us to back up worth a damn, so I replaced it with a 3-blade Max Prop. I wanted to have both good power in reverse and forward. The prop shop in Alameda sized the prop for the boat at 19" diameter and they set the pitch at 19.5" which corresponds to a blade angle of 28 degrees. The Perkins 4.108 which I think is rated at 45 hp at a max 3600 rpm, would only turn 2400 rpm at full throttle. At 2200 rpm the cruising speed was >7 kn. I related this to a Perkins mechanic at British Marine and said that the prop had been set for the point of maximum torque for the engine. His point was that it should be set so that the engine could deliver its maximum power at the top end of rpm. He changed the pitch to 11", or 18 degrees, and now we get 7kn at about 2600 rpm. That's where we normally run, but at least there is more power available if required. And the greatest improvement is that there is far less prop walk. To me, it seems to me that you may have too small a prop or not enough pitch. On Feb 10, 2007, at 12:52 PM, Bob Walden wrote: > > Howdy; > > Our Cal 39 has a brand-new Yanmar 3jh3e engine, which is rated for > 36 HP continuous at 3650 RPM. Wide-open throttle is rated at 4000 > RPM, which according to the specs should generate 40 HP. > > Diesel mechanic said the RPM gauge is calibrated correctly and the > engine is running fine, so we're fairly confident that we're > getting the rated HP to the shaft. > > Hull speed for this boat, based on a LWL of 32' 1" from the sales > specs, should be around 7.6 knots. > > When sailing In 10-12 knots on a reach, this boat bombs along at > over 8 knots, so I know its an easily-driven hull shape, more than > capable of reaching hull speed. > > We have a reversing prop, don't know the type, a picture is > attached. Have not measured the prop, but estimate that the 3 > blades are about 5 or 6 inches from base to tip, and about 4 to 5 > inches across at widest point. Hard to estimate pitch. The > reversing mechanism works well. If anyone recognizes the type of > prop, would appreciate some info on it. > > All of the above is for background info. > > Now: on our boat, 3600 RPM in flat water and a clean hull gets us > up to about 6.5 knots. Haven't really pushed it to WOT for very > long, but it doesn't add much to the speed, maybe goes up to around > 7 knots at best. We're suspecting that the prop is not pitched > correctly or is undersized, or both. We'd like it to be more > efficient, not because we want to water-ski, but for motoring to > weather offshore when the seas are rough. > > OTOH, maybe the engine is too small? > > Would appreciate any input mainly from other cal 39 owners who may > have done adjustments on their props or changed their HP during > repowers, or who can compare their top cruising speeds to ours. At > this point it's a minor issue but we'd like to know what we're > facing if we decide to work on it. > > Thanks! > > bw > Cal 39-2 #003 "Sea Star" > SF Bay > > > <prop.jpg>

It looks like a Luke prop. Joe DeMers Sound Marine Diesel LLC www.soundmarinediesel.com From: "Bob Walden" <bo… [at] bobwalden.com> To: <Ca… [at] yahoogroups.com> Sent: Sunday, February 11, 2007 11:31 AM Subject: Re: [Cal_Boats] Re: Sizing props > hmmm. no, we haven't cleaned it up much, but when it was out of the water > during the survey we looked it over pretty good and did some scraping > looking for markings, didn't find any. I guess next haulout we'll have to > spend more time cleaning it and taking pics. > > ----- Original Message ----- > From: "mtkennedy1" <mt… [at] cox.net> > To: <Ca… [at] yahoogroups.com> > Sent: Sunday, February 11, 2007 7:49 AM > Subject: [Cal_Boats] Re: Sizing props > > > > --- In Ca… [at] yahoogroups.com, "Bob Walden" <bob@...> wrote: > >> > >> thanks Mike. Didn't look like the pics on maxprop's website, I never > >> would > >> have guessed. > >> > >> ----- Original Message ----- > >> From: "mtkennedy1" <mtkennedy1@...> > >> To: <Ca… [at] yahoogroups.com> > >> Sent: Saturday, February 10, 2007 8:38 PM > >> Subject: [Cal_Boats] Re: Sizing props > >> > >> > >> > --- In Ca… [at] yahoogroups.com, "Bob Walden" <bob@> wrote: > >> >> > >> >> well, it's actually a 3-bladed prop--see this pic. > >> > > >> > Three blade MaxProp. Same difference. > > > > I could be wrong about the brand. Maybe there are lookalikes, as there are > > for Martecs. > > Still, the sizing rules should apply. Have you cleaned off the prop and > > looked for any ID ? I > > had a prop that I thought was a Martec but the Martec people pointed out > > it was an > > imitation made by Michigan Wheel. > > > > Mike Kennedy > > Conquest Cal 40 # 96 > > > > > > > > > > > > > > Yahoo! Groups Links > > > > > > > > > > > > > > > Yahoo! Groups Links > > >

Thanks Steve & Kathy, good info. ----- Original Message ----- From: Steve & Kathy Terry To: Ca… [at] yahoogroups.com Sent: Sunday, February 11, 2007 10:48 PM Subject: Re: [Cal_Boats] Sizing props Bob, When we bought our Cal 39 six years ago, it had a 2-blade folding prop that didn't allow us to back up worth a damn, so I replaced it with a 3-blade Max Prop. I wanted to have both good power in reverse and forward. The prop shop in Alameda sized the prop for the boat at 19" diameter and they set the pitch at 19.5" which corresponds to a blade angle of 28 degrees. The Perkins 4.108 which I think is rated at 45 hp at a max 3600 rpm, would only turn 2400 rpm at full throttle. At 2200 rpm the cruising speed was >7 kn. I related this to a Perkins mechanic at British Marine and said that the prop had been set for the point of maximum torque for the engine. His point was that it should be set so that the engine could deliver its maximum power at the top end of rpm. He changed the pitch to 11", or 18 degrees, and now we get 7kn at about 2600 rpm. That's where we normally run, but at least there is more power available if required. And the greatest improvement is that there is far less prop walk. To me, it seems to me that you may have too small a prop or not enough pitch. On Feb 10, 2007, at 12:52 PM, Bob Walden wrote: Howdy; Our Cal 39 has a brand-new Yanmar 3jh3e engine, which is rated for 36 HP continuous at 3650 RPM. Wide-open throttle is rated at 4000 RPM, which according to the specs should generate 40 HP. Diesel mechanic said the RPM gauge is calibrated correctly and the engine is running fine, so we're fairly confident that we're getting the rated HP to the shaft. Hull speed for this boat, based on a LWL of 32' 1" from the sales specs, should be around 7.6 knots. When sailing In 10-12 knots on a reach, this boat bombs along at over 8 knots, so I know its an easily-driven hull shape, more than capable of reaching hull speed. We have a reversing prop, don't know the type, a picture is attached. Have not measured the prop, but estimate that the 3 blades are about 5 or 6 inches from base to tip, and about 4 to 5 inches across at widest point. Hard to estimate pitch. The reversing mechanism works well. If anyone recognizes the type of prop, would appreciate some info on it. All of the above is for background info. Now: on our boat, 3600 RPM in flat water and a clean hull gets us up to about 6.5 knots. Haven't really pushed it to WOT for very long, but it doesn't add much to the speed, maybe goes up to around 7 knots at best. We're suspecting that the prop is not pitched correctly or is undersized, or both. We'd like it to be more efficient, not because we want to water-ski, but for motoring to weather offshore when the seas are rough. OTOH, maybe the engine is too small? Would appreciate any input mainly from other cal 39 owners who may have done adjustments on their props or changed their HP during repowers, or who can compare their top cruising speeds to ours. At this point it's a minor issue but we'd like to know what we're facing if we decide to work on it. Thanks! bw Cal 39-2 #003 "Sea Star" SF Bay <prop.jpg>

Bob, My 29 year old 50 HP 4-108 pushes the boat at about 6.5 kts at 2400 rpm/max throttle at average wave conditions and little wind. I have a 20" flex-o-fold 2 blade prop which works a bit better than the original martec fixed 2 blade prop (smoother and a little more apparent thrust in fwd). Your speed under power seems comparable. My Borg Warner velvet drive transmission has a 2:1 reduction (if I remember correctly); I suspect yours has about 3:1 to give a comparable propeller RPM. I generally cruise at 1800 RPM at around 6 kts. Have you checked the accuracy of your speed log at various heel angles? My speed transducer (mounted near under the L section of the port settee) reads several knots high on a starboard tack and about right on port. Check against the GPS speed when the currents are low -- not so easy on the Bay -- (slack water in the south bay or the Alameda channel?) and run in opposite directions to average out the current. Regards, Duane Duane & Lynn Knize Marlyn, 1978 Cal 2-39, #18 Berthed: Emeryville, CA At 12:52 PM 2/10/2007, you wrote: >Howdy; > >Our Cal 39 has a brand-new Yanmar 3jh3e engine, which is rated for >36 HP continuous at 3650 RPM. Wide-open throttle is rated at 4000 >RPM, which according to the specs should generate 40 HP. > >Diesel mechanic said the RPM gauge is calibrated correctly and the >engine is running fine, so we're fairly confident that we're getting >the rated HP to the shaft. > >Hull speed for this boat, based on a LWL of 32' 1" from the sales >specs, should be around 7.6 knots. > >When sailing In 10-12 knots on a reach, this boat bombs along at >over 8 knots, so I know its an easily-driven hull shape, more than >capable of reaching hull speed. > >We have a reversing prop, don't know the type, a picture is >attached. Have not measured the prop, but estimate that the 3 blades >are about 5 or 6 inches from base to tip, and about 4 to 5 inches >across at widest point. Hard to estimate pitch. The reversing >mechanism works well. If anyone recognizes the type of prop, would >appreciate some info on it. > >All of the above is for background info. > >Now: on our boat, 3600 RPM in flat water and a clean hull gets us up >to about 6.5 knots. Haven't really pushed it to WOT for very long, >but it doesn't add much to the speed, maybe goes up to around 7 >knots at best. We're suspecting that the prop is not pitched >correctly or is undersized, or both. We'd like it to be more >efficient, not because we want to water-ski, but for motoring to >weather offshore when the seas are rough. > >OTOH, maybe the engine is too small? > >Would appreciate any input mainly from other cal 39 owners who may >have done adjustments on their props or changed their HP during >repowers, or who can compare their top cruising speeds to ours. At >this point it's a minor issue but we'd like to know what we're >facing if we decide to work on it. > >Thanks! > >bw >Cal 39-2 #003 "Sea Star" >SF Bay > Duane & Lynn Knize Marlyn, 1978 Cal 2-39, #18 Berthed: Emeryville, CA

When installed in a displacement hull, the 4-108 is factory derated to 40hp @ 3000 rpm. Joe DeMers Sound Marine Diesel LLC www.soundmarinediesel.com ----- Original Message ----- From: Duane Knize To: Ca… [at] yahoogroups.com Sent: Monday, February 12, 2007 1:41 PM Subject: Re: [Cal_Boats] Sizing props (Bob) Bob, My 29 year old 50 HP 4-108 pushes the boat at about 6.5 kts at 2400 rpm/max throttle at average wave conditions and little wind. I have a 20" flex-o-fold 2 blade prop which works a bit better than the original martec fixed 2 blade prop (smoother and a little more apparent thrust in fwd). Your speed under power seems comparable. My Borg Warner velvet drive transmission has a 2:1 reduction (if I remember correctly); I suspect yours has about 3:1 to give a comparable propeller RPM. I generally cruise at 1800 RPM at around 6 kts. Have you checked the accuracy of your speed log at various heel angles? My speed transducer (mounted near under the L section of the port settee) reads several knots high on a starboard tack and about right on port. Check against the GPS speed when the currents are low -- not so easy on the Bay -- (slack water in the south bay or the Alameda channel?) and run in opposite directions to average out the current. Regards, Duane Duane & Lynn Knize Marlyn, 1978 Cal 2-39, #18 Berthed: Emeryville, CA At 12:52 PM 2/10/2007, you wrote: Howdy; Our Cal 39 has a brand-new Yanmar 3jh3e engine, which is rated for 36 HP continuous at 3650 RPM. Wide-open throttle is rated at 4000 RPM, which according to the specs should generate 40 HP. Diesel mechanic said the RPM gauge is calibrated correctly and the engine is running fine, so we're fairly confident that we're getting the rated HP to the shaft. Hull speed for this boat, based on a LWL of 32' 1" from the sales specs, should be around 7.6 knots. When sailing In 10-12 knots on a reach, this boat bombs along at over 8 knots, so I know its an easily-driven hull shape, more than capable of reaching hull speed. We have a reversing prop, don't know the type, a picture is attached. Have not measured the prop, but estimate that the 3 blades are about 5 or 6 inches from base to tip, and about 4 to 5 inches across at widest point. Hard to estimate pitch. The reversing mechanism works well. If anyone recognizes the type of prop, would appreciate some info on it. All of the above is for background info. Now: on our boat, 3600 RPM in flat water and a clean hull gets us up to about 6.5 knots. Haven't really pushed it to WOT for very long, but it doesn't add much to the speed, maybe goes up to around 7 knots at best. We're suspecting that the prop is not pitched correctly or is undersized, or both. We'd like it to be more efficient, not because we want to water-ski, but for motoring to weather offshore when the seas are rough. OTOH, maybe the engine is too small? Would appreciate any input mainly from other cal 39 owners who may have done adjustments on their props or changed their HP during repowers, or who can compare their top cruising speeds to ours. At this point it's a minor issue but we'd like to know what we're facing if we decide to work on it. Thanks! bw Cal 39-2 #003 "Sea Star" SF Bay Duane & Lynn Knize Marlyn, 1978 Cal 2-39, #18 Berthed: Emeryville, CA

Thanks Duane. ----- Original Message ----- From: Duane Knize To: Ca… [at] yahoogroups.com Sent: Monday, February 12, 2007 10:41 AM Subject: Re: [Cal_Boats] Sizing props (Bob) Bob, My 29 year old 50 HP 4-108 pushes the boat at about 6.5 kts at 2400 rpm/max throttle at average wave conditions and little wind. I have a 20" flex-o-fold 2 blade prop which works a bit better than the original martec fixed 2 blade prop (smoother and a little more apparent thrust in fwd). Your speed under power seems comparable. My Borg Warner velvet drive transmission has a 2:1 reduction (if I remember correctly); I suspect yours has about 3:1 to give a comparable propeller RPM. I generally cruise at 1800 RPM at around 6 kts. Have you checked the accuracy of your speed log at various heel angles? My speed transducer (mounted near under the L section of the port settee) reads several knots high on a starboard tack and about right on port. Check against the GPS speed when the currents are low -- not so easy on the Bay -- (slack water in the south bay or the Alameda channel?) and run in opposite directions to average out the current. Regards, Duane Duane & Lynn Knize Marlyn, 1978 Cal 2-39, #18 Berthed: Emeryville, CA At 12:52 PM 2/10/2007, you wrote: Howdy; Our Cal 39 has a brand-new Yanmar 3jh3e engine, which is rated for 36 HP continuous at 3650 RPM. Wide-open throttle is rated at 4000 RPM, which according to the specs should generate 40 HP. Diesel mechanic said the RPM gauge is calibrated correctly and the engine is running fine, so we're fairly confident that we're getting the rated HP to the shaft. Hull speed for this boat, based on a LWL of 32' 1" from the sales specs, should be around 7.6 knots. When sailing In 10-12 knots on a reach, this boat bombs along at over 8 knots, so I know its an easily-driven hull shape, more than capable of reaching hull speed. We have a reversing prop, don't know the type, a picture is attached. Have not measured the prop, but estimate that the 3 blades are about 5 or 6 inches from base to tip, and about 4 to 5 inches across at widest point. Hard to estimate pitch. The reversing mechanism works well. If anyone recognizes the type of prop, would appreciate some info on it. All of the above is for background info. Now: on our boat, 3600 RPM in flat water and a clean hull gets us up to about 6.5 knots. Haven't really pushed it to WOT for very long, but it doesn't add much to the speed, maybe goes up to around 7 knots at best. We're suspecting that the prop is not pitched correctly or is undersized, or both. We'd like it to be more efficient, not because we want to water-ski, but for motoring to weather offshore when the seas are rough. OTOH, maybe the engine is too small? Would appreciate any input mainly from other cal 39 owners who may have done adjustments on their props or changed their HP during repowers, or who can compare their top cruising speeds to ours. At this point it's a minor issue but we'd like to know what we're facing if we decide to work on it. Thanks! bw Cal 39-2 #003 "Sea Star" SF Bay Duane & Lynn Knize Marlyn, 1978 Cal 2-39, #18 Berthed: Emeryville, CA