blaniac

I have a 29' twin step 'V' with twin Merc 496 Mags (375HP) with XR drives running about 72 mph in fresh water on 26p Bravo 4 blades at 5000rpm. Boat weighs about 7,800 lbs.

I have upgraded the motors to 600+HP each and was curious to know what props I should consider. Are the Hydromotive's good for my setup or should I just run some larger Bravo 4 blades? Mercury Maximus a consideration ??

tcelano

Here is what I got for a first cut on your boat, guessing at the pertinent information:

Model: 29

Length: 29 ft

Beam: 8 ft 6 in

Weight: 7500 lb

Deadrise Angle: 24 deg

Hull Depth: 5 ft

Number of Running Strakes: 2

Number of Transverse Ventilated Steps: 2

Hull has a keelpad

Boat has an open cockpit

Engine information:

Boat has 2 x 496 c.i. Normal engines installed

Engine Redline: 5200 RPM

Peak BHP is 375 BHP occuring at 5100 RPM

Peak Torque is 410 lb-ft occuring at 4400 RPM

Drive information:

Boat has 2 x Bravo One, X, XZ, XR Drives Installed, with 1.5:1 gears

Propeller information:

Propeller: 4 bladed Bravo 1

Prop Diameter: 15.25 in

Prop Pitch: 26 in

Prop is set 24 inches behind, and 7 inches below the running surface

Environmental Conditions:

Boat is to be simulated operating in Fresh Water, at 1000 ft above msl, with an ambient air temperature of 80 degrees F

Program Completed

Computational Results
Your boat's computed performance is as follows:

SPEED(mph) ENGINE RPM REQ'D BHP AVAILABLE BHP PROP SLIP WETTED LENGTH(ft)

26.00 2235 142 312 30.19 18.93
27.00 2294 149 322 29.38 18.54
28.00 2354 156 332 28.61 18.19
29.00 2415 163 342 27.89 17.85
30.00 2473 170 352 27.15 17.35
31.00 2533 177 363 26.51 17.05
32.00 2592 184 373 25.84 16.59
33.00 2653 193 384 25.27 16.34
34.00 2711 200 394 24.66 15.92
35.00 2772 209 405 24.15 15.70
36.00 2831 217 415 23.60 15.31
37.00 2890 226 425 23.07 14.94
38.00 2952 235 436 22.63 14.76
39.00 3011 244 446 22.14 14.42
40.00 3070 253 456 21.68 14.09
41.00 3129 262 467 21.24 13.77
42.00 3191 273 477 20.88 13.64
43.00 3250 283 487 20.48 13.34
44.00 3310 292 497 20.09 13.06
45.00 3369 303 507 19.71 12.79
46.00 3432 314 518 19.41 12.69
47.00 3492 325 527 19.07 12.44
48.00 3552 336 537 18.74 12.19
49.00 3611 347 546 18.42 11.96
50.00 3671 358 556 18.12 11.73
51.00 3732 369 565 17.82 11.51
52.00 3792 381 574 17.54 11.30
53.00 3855 395 583 17.32 11.24
54.00 3915 407 591 17.06 11.04
55.00 3976 420 600 16.80 10.85
56.00 4036 433 608 16.56 10.66
57.00 4097 446 615 16.33 10.48
58.00 4157 459 623 16.10 10.31
59.00 4218 473 630 15.88 10.14
60.00 4279 487 637 15.67 9.980
61.00 4340 501 643 15.46 9.821
62.00 4404 518 650 15.31 9.790
63.00 4465 532 655 15.12 9.639
64.00 4526 548 661 14.93 9.491
65.00 4587 563 666 14.76 9.348
66.00 4648 579 670 14.58 9.209
67.00 4709 595 674 14.42 9.074
68.00 4770 611 678 14.25 8.943
69.00 4832 628 681 14.10 8.815
70.00 4893 645 683 13.95 8.690
71.00 4955 662 685 13.80 8.569
72.00 5016 680 686 13.66 8.450
72.37 5039 687 687 13.52 8.335
Thank You for using www.SpeedboatPerformance.com!!

Making some more assumptions about how you are getting to 600 hp:

Model: 29

Length: 29 ft

Beam: 8 ft 6 in

Weight: 7500 lb

Deadrise Angle: 24 deg

Hull Depth: 5 ft

Number of Running Strakes: 2

Number of Transverse Ventilated Steps: 2

Hull has a keelpad

Boat has an open cockpit

Engine information:

Boat has 2 x 496 c.i. Supercharged/Intercooled engines installed

Engine Redline: 5400 RPM

Peak BHP is 600 BHP occuring at 5400 RPM

Peak Torque is 650 lb-ft occuring at 4500 RPM

Drive information:

Boat has 2 x Bravo One, X, XZ, XR Drives Installed, with 1.5:1 gears

Propeller information:

Propeller: 4 bladed Bravo 1

Prop Diameter: 15.25 in

Prop Pitch: 33 in

Prop is set 24 inches behind, and 7 inches below the running surface

Environmental Conditions:

Boat is to be simulated operating in Fresh Water, at 1000 ft above msl, with an ambient air temperature of 80 degrees F

Program Completed

Computational Results
Your boat's computed performance is as follows:

SPEED(mph) ENGINE RPM REQ'D BHP AVAILABLE BHP PROP SLIP WETTED LENGTH(ft)

26.00 1969 163 354 37.59 18.93
27.00 2016 169 365 36.67 18.54
28.00 2063 176 377 35.80 18.19
29.00 2110 183 388 34.98 17.85
30.00 2155 188 400 34.14 17.35
31.00 2203 196 412 33.41 17.05
32.00 2248 202 423 32.64 16.59
33.00 2296 209 436 31.98 16.34
34.00 2342 216 448 31.28 15.92
35.00 2390 224 460 30.68 15.70
36.00 2436 231 473 30.05 15.31
37.00 2482 239 485 29.44 14.94
38.00 2531 248 498 28.92 14.76
39.00 2578 256 511 28.36 14.42
40.00 2624 264 523 27.83 14.09
41.00 2671 272 536 27.31 13.77
42.00 2721 282 550 26.89 13.64
43.00 2768 291 562 26.41 13.34
44.00 2815 300 575 25.96 13.06
45.00 2862 310 589 25.52 12.79
46.00 2912 321 603 25.17 12.69
47.00 2959 331 616 24.77 12.44
48.00 3007 342 629 24.38 12.19
49.00 3054 352 642 24.00 11.96
50.00 3102 363 656 23.64 11.73
51.00 3150 374 669 23.30 11.51
52.00 3198 386 682 22.96 11.30
53.00 3249 399 697 22.70 11.24
54.00 3297 411 710 22.39 11.04
55.00 3345 423 723 22.09 10.85
56.00 3393 436 737 21.80 10.66
57.00 3442 449 750 21.52 10.48
58.00 3490 462 763 21.25 10.31
59.00 3538 475 776 20.99 10.14
60.00 3587 489 790 20.74 9.980
61.00 3636 503 803 20.50 9.821
62.00 3688 519 816 20.32 9.790
63.00 3736 534 829 20.09 9.639
64.00 3785 549 842 19.87 9.491
65.00 3834 564 855 19.66 9.348
66.00 3883 579 867 19.45 9.209
67.00 3932 595 879 19.25 9.074
68.00 3982 611 891 19.06 8.943
69.00 4031 628 903 18.87 8.815
70.00 4080 645 915 18.69 8.690
71.00 4130 662 927 18.52 8.569
72.00 4179 679 938 18.35 8.450
73.00 4229 697 949 18.18 8.335
74.00 4278 715 960 18.02 8.223
75.00 4328 734 970 17.87 8.113
76.00 4377 753 981 17.72 8.007
77.00 4427 772 991 17.57 7.902
78.00 4477 791 1000 17.43 7.801
79.00 4527 811 1010 17.29 7.702
80.00 4580 835 1019 17.19 7.705
81.00 4630 856 1028 17.06 7.609
82.00 4680 877 1036 16.94 7.515
83.00 4730 898 1044 16.81 7.424
84.00 4780 920 1051 16.69 7.334
85.00 4830 943 1058 16.58 7.247
86.00 4880 966 1064 16.46 7.161
87.00 4930 989 1070 16.35 7.077
88.00 4981 1012 1076 16.25 6.995
89.00 5031 1036 1081 16.14 6.915
90.00 5081 1061 1085 16.04 6.837
91.00 5132 1086 1089 15.94 6.760
91.26 5145 1092 1092 15.84 6.684
Click here to return to Simulate! page
Thank You for using www.SpeedboatPerformance.com!!


I think you are still well within the realm of a Bravo 1 prop. (32-33" depending on what the redline will be on the upgraded motors). Without upgrades to your drives, going to the 5-blade prop may be more extra stress on the drives than you need or want, although this setup still seems to have quite a lot of prop slip for a relatively light twin engine boat. What I have found in my studies are regions of good operating efficiency in the 15% slip range, and another in the 8% range (for most props). For some reason, the middle ground isn't quite as good. Going out past 20% is very bad, and less than 8% means you are dragging way too much blade through the water.

Go try http://www.speedboatperformance.com for yourself; it's free! Definitely post your results after some on-the water testing. You might consider swapping lower units for some -1 or -2" shorties with sportmaster type gearcases if you really want to take full advantage of your newfound horsepower! My calcs show you could see near 96 mph with 34" props.

Another thing to consider, though. Your boat's longitudinal center of gravity was set up to optimize performance and handling at slower speeds. You may be balanced too bow heavy to see the speeds we're talking about here. If you are using a bit of trim tab now, you might be fine, but you are going to want props that give you a bit of bow lift, most likely. The Hydromotives generally are famous for stern-lift. This is all based on guesswork and generalities, without even knowing the hull you have, but these are just some things to think about.

blaniac

Wow, you had me at "Hello" !!!

I bought a pair of labbed 34's, so maybe that will get me close to the 33 projections. I like the idea of maybe shorties with the sportmaster lowers. Just trying not to keep on dumping more $$ into the project that I don't really need to.

The 600 HP is not coming from a blower or supercharger and max rpm will still be at 5100 for the time being.
www.raylarengine.com

Thanks

tcelano

Yes, you should be perfect with labbed 34's and 5100 RPM. Here's the prediction with those and the stock B1 gearcases: Slip numbers are up a little higher than I'd like, but you should gain 3 or so mph over the stock 33's! You are definitely getting into the region where Sportmasters would help, but that's something that can be swapped at any time.

I put years of work into making the prediction code work as part of my research, so I'm glad when it can be used for good. For me, it's the next best thing when I'm not out running my boat!

Model: 29

Length: 29 ft

Beam: 8 ft 6 in

Weight: 7500 lb

Deadrise Angle: 24 deg

Hull Depth: 5 ft

Number of Running Strakes: 2

Number of Transverse Ventilated Steps: 2

Hull has a keelpad

Boat has an open cockpit

Engine information:

Boat has 2 x 496 c.i. Normal engines installed

Engine Redline: 5200 RPM

Peak BHP is 600 BHP occuring at 5100 RPM

Peak Torque is 660 lb-ft occuring at 4500 RPM

Drive information:

Boat has 2 x Bravo One, X, XZ, XR Drives Installed, with 1.5:1 gears

Propeller information:

Propeller: 4 bladed Bravo 1 Lab Finished

Prop Diameter: 15.25 in

Prop Pitch: 34 in

Prop is set 24 inches behind, and 7 inches below the running surface

Environmental Conditions:

Boat is to be simulated operating in Fresh Water, at 1000 ft above msl, with an ambient air temperature of 80 degrees F

Program Completed

Computational Results
Your boat's computed performance is as follows:

SPEED(mph) ENGINE RPM REQ'D BHP AVAILABLE BHP PROP SLIP WETTED LENGTH(ft)

26.00 1963 171 427 40.95 18.93
27.00 2006 178 438 39.98 18.54
28.00 2049 185 450 39.06 18.19
29.00 2093 192 461 38.19 17.85
30.00 2134 198 472 37.30 17.35
31.00 2178 205 484 36.51 17.05
32.00 2220 211 495 35.70 16.59
33.00 2265 218 507 34.99 16.34
34.00 2307 224 519 34.24 15.92
35.00 2353 232 531 33.61 15.70
36.00 2395 238 543 32.92 15.31
37.00 2438 245 554 32.27 14.94
38.00 2484 253 567 31.71 14.76
39.00 2527 261 579 31.11 14.42
40.00 2571 268 591 30.53 14.09
41.00 2614 275 603 29.98 13.77
42.00 2661 285 616 29.52 13.64
43.00 2705 293 628 29.01 13.34
44.00 2749 301 641 28.52 13.06
45.00 2793 310 653 28.04 12.79
46.00 2840 321 666 27.66 12.69
47.00 2884 330 679 27.22 12.44
48.00 2929 339 691 26.80 12.19
49.00 2973 349 703 26.39 11.96
50.00 3018 359 716 26.00 11.73
51.00 3063 369 728 25.62 11.51
52.00 3107 379 741 25.26 11.30
53.00 3156 392 754 24.97 11.24
54.00 3201 403 766 24.63 11.04
55.00 3246 415 778 24.30 10.85
56.00 3291 426 791 23.99 10.66
57.00 3337 438 803 23.68 10.48
58.00 3382 450 815 23.38 10.31
59.00 3428 462 827 23.10 10.14
60.00 3473 475 839 22.82 9.980
61.00 3519 488 851 22.56 9.821
62.00 3568 504 863 22.36 9.790
63.00 3614 517 875 22.11 9.639
64.00 3660 531 886 21.86 9.491
65.00 3706 545 897 21.63 9.348
66.00 3752 559 908 21.40 9.209
67.00 3798 574 919 21.18 9.074
68.00 3845 589 930 20.97 8.943
69.00 3891 604 941 20.76 8.815
70.00 3938 620 951 20.56 8.690
71.00 3984 636 961 20.37 8.569
72.00 4031 652 971 20.18 8.450
73.00 4077 668 981 19.99 8.335
74.00 4124 685 990 19.82 8.223
75.00 4171 702 999 19.64 8.113
76.00 4218 720 1008 19.48 8.007
77.00 4264 737 1016 19.31 7.902
78.00 4311 756 1025 19.16 7.801
79.00 4358 774 1032 19.00 7.702
80.00 4409 796 1040 18.90 7.705
81.00 4456 815 1047 18.75 7.609
82.00 4503 835 1054 18.61 7.515
83.00 4550 855 1060 18.47 7.424
84.00 4597 875 1066 18.34 7.334
85.00 4645 896 1072 18.21 7.247
86.00 4692 917 1077 18.08 7.161
87.00 4740 938 1081 17.96 7.077
88.00 4787 960 1086 17.84 6.995
89.00 4835 982 1089 17.72 6.915
90.00 4882 1004 1092 17.61 6.837
91.00 4930 1027 1095 17.50 6.760
92.00 4978 1050 1097 17.39 6.684
93.00 5025 1074 1098 17.28 6.611
94.00 5073 1098 1099 17.18 6.538
94.04 5075 1099 1099 17.08 6.467
Click here to return to Simulate! page
Thank You for using www.SpeedboatPerformance.com!!

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throttleup

Blaniac,

Starting with your current numbers; The 375 496 has a rev limiter at 4900, how are you getting 5000, did you have the computer re-programmed? Your current slip is very low, 9% at 5000 rpm and only 6% if the rev limiter is still at 4900 rpm. Are your speeds from GPS or radar? Did you run them in both directions and average the speed?

If you are building a naturally aspirated 496 to produce 600 HP you are going to have to turn some rpm. I would estimate you will need to turn about 5800-6000 rpm to get 600 hp from the 496. If this is the case running the motors at 5100 is going to result in a small speed gain from where you are now and with 34 pitch props@5100 WOT you will most likely have some serious handling issues.

To get the most from your new motors my guess would be to turn the motors at 5900 rpm with 28 Bravo 1's with a top speed of about 88-90.

Matt

blaniac

Just wondering if a 32p might be better for getting on plane and midrange acceleration, without sacrificing too much on the top

blaniac

Matt

I will ask Ray from Raylar to respond to your comments here as I am not equipped to do so but curious of the answers. I do know that we are using HO ecm's that get us the higher rev limiter and they are working on getting it even higher. The engines produce 600HP well before the 5100 that I recall seeing on the dyno sheets.

cobra marty

88-90mph and 96mph or 5900rpm yea right maybe downhill. Don't let them set you up for disappointment. Forget about HP numbers and look at Torque numbers. This is why we build 500 HP 500CID motors and not 500HP 2liter Honda motors. Realistically you need 12-20 lb-ft of Torque to go 1 mph faster(12 in the 50-60range and 20 in the 80-90range). Right now you are doing 72 with about ?1060TQ(?530 each stock 375HP motor) and you will have about 1260TQ(per Raylar 630TQ at 5000rpm). So you have 200 lb-ft of Torque to do more work, that is, to go faster. So according to the 12-20TQ for 1 mph you will go 10-14 mph faster and need to prop accordingly. So with 4mph for every 2" increased pitch, I would think that you will need a 28" and have it labbed or a little more engine rpm or a max of 30". I would start with a pair of stock 30" bravo props and see where you are with WOT and MPH or a set of 28" but I think you will be all over the rev limiter unless it has been raised. I say 85-86mph max. I can't wait and see. When do you splash the boat?
And you don't need 5 blades until your prop height is so high that you can blow out the 4 blades.

throttleup

Sounds great. Take a look at the dyno sheets and see if it's peak torque or peak HP that's produced before 5100. Seems like it would take more than 5100 rpm to get that kind of HP from 496 ci, but I'm not an engine builder. There are others here on the board who could answer that question much better than I can.

You will want to make sure you stay away from running the motor at WOT when it's at peak torque, or close to it. That's where you will get unpredictable handling problems and high slip numbers.

Matt

Raylar

Blaniac has asked me to wade in here. Matt, on our new HO600 496 we are indeed producing 600HP at 5100 rpms and about 630-640 ft. lbs of torque at the torque peak at 4100 rpms. We do have about 540 ft/lbs of torque at 2300 rpms and the motor still produces about 525 ft/lbs at 5100 rpms so the torque curve is fairly flat and high. The stock rev limiter on the HO ecm's we are using for the conversion have the rev limiter set at 5150 and we will be turning them up later to about 5400. The engine produces peak HP at 5300 which is about 613 HP. I think from the numbers we have seen on Blaniac's boat that his Bravo's seem to be set at good x-heights and the boat seems to generate very good speed per HP/TQ. I think I would tend to agree that a prop in the 28P-30P pitch range may be the best choice. Would he be better off to use the 30P un-labbed and then lab them for his top rpm? I am not any kind of prop expert so I will leave it to you, you guys know far more about props than most anyone and I think its really important for Blaniac to work with someone like yourself to get his boat dialed in with the new power of our Raylar motors. Cobra Marty, thanks for your insight here two, you have years of real world expierence to share!

Thanks for the Help, greatly appreciated!
Ray @ Raylar