Would I benefit from re-propping?

[Southpaw II]

You can see my boat from the sig, but here's the question...My boat came from the Northeast (Long Island) and I bought it from the second owner after he retired to Tampa, FL...I think he just didn't enjoy boating there like he did on Long Island.

Anyway, the boat originally had 7.4 Horizons, but was repowered, under warranty in 2003 with 8.1 Horizons...new engines and new exhaust system. It was a water intrusion issue. Anyway, no problems now.

When I throttle down on this boat, it leaps. It lifts, and goes....and I think it could use more pitch on the props, but I don't want to overload the transmissions. The props are original, 21x22 4-blade HyTorqs.

I've been on other similar boats that don't seem to have the torque that this boat does. The boat runs the 4800 rpm that it is supposed to run, and my speeds are similar to the other posts on here that others see.

Sea Ray made several models from the 2000-2002 era that went from the 7.4 to the 8.1. Did they keep the same prop with the 8.1 that was used on the boats with the 7.4L engines?


I guess, that because the boat "feels" under propped, and I wonder if the 8.1 L boats are propped different than the 7.4 L boats.....and, is there any real difference between the 7.4 and the 8.1 as far as torque is concerned?

 

[mistercomputerman]

I had the same questions about my 410DA. Here is what Sea Ray sent me in response to my inquiries. I would give them a shout and see if they might have the same info on your 380DA.

MODEL/ENGINE SPECIFICATIONS
W/PERFORMANCE TEST
(TO BE USED AS REFERENCE ONLY)
2001 410DA
MERC 7.4L MPI HORIZON T-380​

OVERALL LENGTH: 41'6"
LENGTH W/ BOW PULPIT:
LENGTH W/ SWIM PLATFORM: 45'6"
BEAM: 13'10"
DRAFT (INBOARDS): 38"
DRAFT (STERNDRIVE DOWN):
DRAFT (STERNDRIVE UP):
DEADRISE (DEGREES): 19
{1} DRY WEIGHT: 22,000 POUNDS
WATER CAPACITY: 100 GALLONS
FUEL CAPACITY: 335 GALLONS
OVERALL HEIGHT FROM WATERLINE: 121"SP (W=WINDSHIELD, SP=SPOILER
OVERALL HEIGHT FROM KEEL: 153"SP HT=HARD TOP, V=VENTURI)


MERC 7.4L HORIZON: T-380
TRANSMISSION / GEAR: HURTH 630V
{2} SHAFT (DIAMETER x LENGTH): 1.5" x 78"
PROP SIZE (DIAMETER x PITCH): 21 x 21 4BC NIBRAL (C=CUPPED, S=STRAIGHT)
GEAR REDUCTION RATIO: 2.50:1


{3} RPM @ CRUISE: 3000
{4} SPEED @ CRUISE: 17 - 21 MPH
{4} SPEED @ CRUISE: 15 - 18 KNOTS
{5} FUEL USAGE @ CRUISE: 28.2 GPH
W.O.T. RPM: 4800
{4} W.O.T. SPEED: 28 - 33 MPH
{4} W.O.T. SPEED: 24 - 29 KNOTS
{5} FUEL USAGE @ W.O.T.: 64 GPH

*********************************************************************************************

{1} Weight shown is boat with standard engine and most optional equipment.​

{2} Shaft length is from coupling face to shaft end.
{3} CRUISE RPM shown is a selected base to be used as reference. Actual cruising RPM may vary from person to person depending on preference.
{4} MPH and KNOTS are calculated using optimum trim of boat with and without using trim tabs. Prop condition can affect speed.
{5} GPH is usage on both engines. Readings are based on engine manufacturer’s dynamometer tests and is to be used as a reference only. Actual operational specs may vary with sea conditions and boat loading.

NOTE: All data recorded at sea level. Variations in loading, altitude, temperature, and sea conditions will affect performance and may result in lower speed and less range.

MODEL/ENGINE SPECIFICATIONS​

W/PERFORMANCE TEST
(TO BE USED AS REFERENCE ONLY)​

2003 410DA
MERC 8.1S HORIZON T-370​

OVERALL LENGTH: 41’6”
LENGTH W/BOW PULPIT:
LENGTH W/SWIM PLATFORM: 45’6”
BEAM: 13’10”
DRAFT (INBOARDS): 40”
DRAFT (STERNDRIVE DOWN):
DRAFT (STERNDRIVE UP):
DEADRISE (DEGREES): 19
{1} DRY WEIGHT: 22,000 POUNDS
WATER CAPACITY: 100 GALLONS
FUEL CAPACITY: 335 GALLONS
OVERALL HEIGHT FROM WATERLINE: 99”W 131"SP (W=WINDSHIELD, SP=SPOILER
OVERALL HEIGHT FROM KEEL: 121"W 153”SP HT=HARD TOP, V=VENTURI)

MERC 8.1S: T-370
TRANSMISSION/GEAR: HURTH 630V1
{2} SHAFT (DIAxLENGTH): 1.5” x 78”
PROP SIZE (DIAxPITCH): 21 x 22 4BLC NIBRAL (C=CUPPED, S=STRAIGHT)
GEAR REDUCTION RATIO: 2.50:1

{3} RPM @ CRUISE: 3250
{4} SPEED @ CRUISE: 18 - 22 MPH
{4} SPEED @ CRUISE: 15.8 - 19 KNOTS
{5} FUEL USAGE @ CRUISE: 32 GPH
W.O.T. RPM: 4600
{4} W.O.T. SPEED: 31 - 35 MPH
{4} W.O.T. SPEED: 27 – 31 KNOTS
{5} FUEL USAGE @ W.O.T.: 61 GPH

*******************************************************************************

{1} Weight shown is boat with standard engine and most optional equipment.

{2} Shaft length is from coupling face to shaft end.

{3} CRUISE RPM shown is a selected base to be used as reference. Actual
cruising RPM may vary from person to person depending on preference.

{4} MPH and KNOTS are calculated using optimum trim of boat with and without
using trim tabs. Prop condition can affect speed.

{5} GPH is usage on both engines. Readings are based on engine manufacturer’s
dynamometer tests and is to be used as a reference only. Actual
operational specs may vary with sea conditions and boat loading.

NOTE: All data recorded at sea level. Variations in loading, altitude, temperature, and sea conditions will affect performance and may result in lower speed and less range.

 

[Southpaw II]

This is good info, thanks. I did get a list of all the serial numbered items issued to my boat from Sea Ray. It had everything from the TVs, radio, microwave, and even engines and trans info. The props on the list were, as I said, 21x22x73 3/16x1 1/2. There were even phone numbers for company contacts.

 

[osd9]

I don't remember the trans numbers/ratios, but my 2002 380DA with 8.1s came from the factory with 21X23 four blade Nibrals with a medium cup.

You WOT of 4800 is definitely on the high side. Not knowing all the facts, but IMHO, I'd say you could add and inch of pitch without any harm....but best to take your trans ratios to a good prop shop and ask him....

 

[dc380]

I cut this from the paperwork Prop shop gave me.

RH/LH labeled: (Hy-Torq) 21 x 23 (port) and 21 x 22.5 (starboard)
​

(4) Blade Nibral w/L-cup ​

My boat also is quick to plane, but I only turn 4400 at WOT.

 

[Southpaw II]

I do have the 2.5:1 trans. Now you are making me think I need to shop for 21x23 props.

So...if I am a bit (only slightly) under-propped, I wonder how it is really affecting my WOT and cruise performance and fuel usage? I know this has been discussed quite a bit, but, not exactly in this context.

Can anybody else out there with 8.1s in a 380DA verify their factory prop size?

 

[dc380]

My documentation shows my transmissions are

A = 2.48:1 / B = 2.53:1

 

[my3sons]

I was shopping 380's and 360's last year and had the spec sheet like the ones posted above for the 8.1 380's. Unfortunately, I deleted it when we bought the 360, but I remember that the prop sizes were the same, and they were as posted by dc380, 21x23 and 21x22.5 Take care

 

[tobnpr]

Too much emphasis on what "factory" props are. It's a starting point only- everyone loads and uses their boat differently. You still need to prop to achieve max rpms.

Don't assume that factory props are correct. If anything, all boat manufacturers tend to size their props with very lightly loaded boats to be able to advertise the best performance numbers. Wouldn't you?

Sea Ray said it themselves in the response posted above.
"Actual operational specs may vary with sea conditions and boat loading."

If you're operating in open ocean conditions, it's not a bad idea on that size boat with gassers to be a bit underpropped. The reserve power will help offshore.

 

[Southpaw II]

So, it seems the 380 DA with the 7.4 L engine gets the 21X22 and the 8.1 L gets the 21X23 props.

WOT numbers are about 2 mph difference @ +/- 4700 rpm and cruise numbers are in the range of +/- 1 mph difference @ 3500 rpm. On my freshwater lake, making short runs, and maybe putting 60 hrs. per year on.....I'm gonna stay put until something forces a change for me. I appreciate the input from you guys.

 

[osd9]

I knew I had this somewhere and I just found it....same type info posted above for the 410DA gasser but specific to the 380DA with 8.1 motors. I got this from SeaRay...

MODEL/ENGINE SPECIFICATIONS


W/PERFORMANCE TEST


(TO BE USED AS REFERENCE ONLY)​

2001


380DA


MERC 8.1S HORIZON


T-370​

OVERALL LENGTH: 38'
LENGTH W/BOW PULPIT:
LENGTH W/SWIM PLATFORM: 41’1”
BEAM: 13’
DRAFT (INBOARDS): 44”
DRAFT (STERNDRIVE DOWN):
DRAFT (STERNDRIVE UP):
DEADRISE (DEGREES): 19.5
{1} DRY WEIGHT: 18,300 POUNDS
WATER CAPACITY: 70 GALLONS
FUEL CAPACITY: 275 GALLONS
OVERALL HEIGHT FROM WATERLINE: 77”W 116"SP (W=WINDSHIELD, SP=SPOILER
OVERALL HEIGHT FROM KEEL: 107"W 151”SP HT=HARD TOP, V=VENTURI)

MERC 8.1S T-370
TRANSMISSION/GEAR: Hurth 630V1
{2} SHAFT (DIAxLENGTH): 1.5” x 73.19”
PROP SIZE (DIAxPITCH): 21 x 23 4BC NOBRAL (C=CUPPED, S=STRAIGHT)
GEAR REDUCTION RATIO: 2.50:1

{3} RPM @ CRUISE: 3000
{4} SPEED @ CRUISE: 17 - 21 MPH
{4} SPEED @ CRUISE: 15 - 18 KNOTS
{5} FUEL USAGE @ CRUISE: 28.2 GPH
W.O.T. RPM: 4600
{4} W.O.T. SPEED: 32 - 36 MPH
{4} W.O.T. SPEED: 28.1 - 31.6 KNOTS
{5} FUEL USAGE @ W.O.T.: 64 GPH

*******************************************************************************

{1} Weight shown is boat with standard engine and most optional equipment.

{2} Shaft length is from coupling face to shaft end.

{3} CRUISE RPM shown is a selected base to be used as reference. Actual
cruising RPM may vary from person to person depending on preference.

{4} MPH and KNOTS are calculated using optimum trim of boat with and without
using trim tabs. Prop condition can affect speed.

{5} GPH is usage on both engines. Readings are based on engine manufacturer’s
dynamometer tests and is to be used as a reference only. Actual
operational specs may vary with sea conditions and boat loading.

NOTE: All data recorded at sea level. Variations in loading, altitude, temperature, and sea conditions will affect performance and may result in lower speed and less range.

 

[Southpaw II]

Interesting....this shows a 3000 rpm cruise with the 21x23. My boat with the 21x22 prop will not cruise that low. Under optimum conditions, absolute minimum is about 3400. 3500 is usually normal for me, and I do about 21.5 kts.