Prop question

"Ok guys ,i went out to the l

"Ok guys ,i went out to the lake today and ran my wellcraft v20 with a SS prop (15x17p)and got up to 3000plus RPMs, at WOT, now before that i was running an aluminum 15x19 and was doing 3500 plus rpms.at WOT , my engine is a straight six 250 (165h.p.) merc.rated i think at 3900 to 4100 rpms, what should i do ? ?whats best? what's more convenient? can i use a 15x19 ss prop instead of the alum. 15x19 . should i go bigger , smaller? you guys tell me.By the way i think i was faster on the alum. than the ss?? is it the pitch?....my speedometer is wacked saids 35 but wind says 100 lol appreciate your help guys . Angel"

"Angel: have you used Rod&#39

"Angel: have you used Rod's prop chart? If you need help using it, I'll do it for you. Send the outdrive gear ratio and loaded boat weight.

Total boat weight w/fuel & passengers.......?

Outdrive gear ratio...........?

Horsepower....................165

Maximum WOT RPMs..............4100

Elevation; I presume you are at sea level


I am running a 15.25" 21 pitch SS prop behind a 175 HP 4.3L V-6 @ 4400 RPM non-vortec. It jumps out of the water onto plane under 3000 RPMs.

If it was my boat, I would try a 15" 21 pitch to see how it did. SS is a stronger low flex prop. Your straight six is a workhorse engine and can handle the SS 21 pitch."

"what year is yer 165hp?

i&

"what year is yer 165hp?

i've had 2, both wot spec at 3900-4300rpm.

when was the last time ya had a tune up done? 3k-3500 is too low and i'd think ya should be able to spin a 17 with the 165 unless yer boat is real heavy....

i'm usein a 19 alum. and get 4300 @wot on a 19' aristocraft...

i was usein a 21p alum. and only gettin 38-3900 wot. it was to big for me i thought....

i'd thinkin something else is up for not gettin to wot spec. ya should be able to do the 17p i'd think."

"Guy;
Just curious, have you

"Guy;
Just curious, have you ever tried a TorqueShift prop with your 4.3? Someone on this site a while back had good luck with one on a 4.3.
BTW, it sounds like you have a sweet running engine. Is it the 1.81 ratio leg?

Rod"

Thanks Rod:

The only number

Thanks Rod:

The only number I found on the OD after turning my head upside down was the Merc. SN tag B759864. My old beast would not run as good as it does w/o the contributions from this board. Thanks everyone.

"Guy;
In truth I think everyo

"Guy;
In truth I think everyone here owes you a big round of thanks. You have contributed way more than you have received, without doubt.

If you are making 40+MPH with a 21P prop and 4400 RPM, you may have a 1.62 drive.

Anyway, happy boating
Rod"

"Angel,

You might consider

"Angel,

You might consider moving to a 4 blade stainless prop particularly if your boat is very heavy.

4 blade prop will give you better "bite".

In my last boat a 4 blade ss 15 x 19 prop out performed the 3 blade alloy props I tried by far and pecularly the additional boat speed at plane allowed the engine to rev more freely.

Someone else with better knowledge might be able to tell you more than I.

I tend to also go with what Jim says... You may have some engine issues too and it would be well worth getting the engine looked at before you spent too much time propping it.

There is another issue that is... if you have not owned the boat from new someone may have changed the leg at some point and given you a different gear ratio which may not suit the boat."

"Ok, guys i found out,my outd

"Ok, guys i found out,my outdrive is a 1.68 to 1 ratio and it saids 165 h.p. on it , the weight on the boat ,i only know is a 20' 76 wellcraft maybe 3500 to 4000 # same as rpms i quess lol?... any way putting all the info. together see what we come up to ,load on the boat when checked for rpms was no pass. no gear just 15 dollars of gas on each tank? with gas $ now, probably 5 gal. on both tanks ...lol just figuring what prop to use with you guys help thanks again guys(the rpms guage is what? 21 years old? quess is tired.. maybe need a younger one . Angel keeping you busy"

"angel, check here for how muc

"angel, check here for how much yer boat may weight. from what i'm seein of 1976 wellcraft boats, yers may weight in at around just under 2000lbs, or just under 3000lbs. ya need to see which model ya got to find out.

http://www.iboats.com/Wellcraft_Boats/bp/20br1527

if yer weightin in at 3500-4k lbs. ya may have found out why yer only gettin 3500rpms w/17p prop....maybe waterloged. if yer tach is suspect, check it against a shop tach....."

"Jim:

Good point on the wat

"Jim:

Good point on the water logged boat. It happened to me with my 87 Baretta 19'. When I went to replace the soft floor in early March 2006, I uncovered a several hundred pound mass of frozen foam. Did the new floor, stringers and transom w/epoxy sealant. Left the foam out. Made a big difference."