TLDI 50 - prop size?

[secross2]

I have a TDLI 50. I'm trying to get the maximum cruising speed. I read somewhere if I have a larger prop put on the 50 it lower RPMs and get more speed. I would imagine the shop would have to change the gear ratio. Did I understand this article correct? I have misplaced the mag.

2. Does any body know what the is rated at? re:speed/knot HP.
I've taked with Macgregor and they just told me what the brochure says, "using the 50 so it has little effect on sailing.
Thanks.......
By the way my wife wants a speed boat,

[parrothead]

You'll find a thread on trying to find the ideal prop for the TLDI 50 at http://macgregorsailors.com/phpBB/viewt ... ght=#59088
including my personal experiences with a 4-bladed prop on our M.

[Frank C]

I have a TDLI 50. I'm trying to get the maximum cruising speed.
..... By the way my wife wants a speed boat,

Important notes regarding props - they are sized by diameter x pitch x blade-count. The 26X or M are relatively heavy cruising boats and the 50-horse motor is fairly small, relative to most powerboats. Therefore, we see top speeds of 15 to 25 mph instead of small cuddy cruisers that might go 30 to 40 mph. After all, this IS a sailboat too!

• Your Nissan TLDI uses up to a 12-inch diameter prop (max diameter).
• Typical pitch for the Mac 26 will be 9 to 11 inches. Pitch is distance fwd with one prop revolution.
• Most here use a 3-bladed prop. A few usually rave about their 4-blades for smoothness & low-speed maneuvers.
• Gearing ratio is fixed within the outboard - yours turns 1.85 rpms for each prop revolution.
• It's tough to predict speed, but your 50, wide-open, 16 to 19 mph - varies w/load & bottom paint;
  ..... those with TLDI 90 (15" diam prop) get up to 28 mph.
• What do you mean by "cruising" speed?
  ... (wife might be happier with a 90-horse)

[secross2]

my concern is burning the 50 out. Can I go 12.14 knots with Mac at 4300rpm for say 6 to 8 hours w/o burning her out?
The motor has very few hours on it. I thought it had 200 but it ends up having approx 80 after tracking the hours.

All we store is cloths, and the basics.

[Frank C]

• I just went to Nissan's website. Their recommended engine speed at WOT is 5200 to 5800 rpms.
• As long as your prop can get you into that range at WOT, it's correctly propped.
• Therefore, continuous operation (3 to 4 hours) at a mid-cruise of 4300 rpm is no issue at all - no problem.

But if your pitch is too great the motor won't be able to reach the recommended max rpms when wide-open, which means that prop is lugging the engine - at all speeds - not good for the engine. This is not Mac specific. It's standard 'prop logic' that you'll read in boating articles across the internet, including MFG websites & owner guides.

[opie]

FrankC - Can you do the same thing for the Honda BF50A engine regarding prop selection and details that you did in this thread for the other engine? Thanks. I looked and read all the other threads last night as I want to buy a new prop at WM's sale that starts today. In the threads I recorded randomly the following sizes for the BF50A:
10.75 x 13 x 3, 11.25 x 13 x 3, 12 x 10.25 x 3, 11.8 x 9 x 3, plus the comments here and there like: "avoid any prop that is cupped", "use a 4-blade if you plan to pull a tube", "ask the dealer for a pontoon boat prop", "get a big-dog-eared prop", "more than 12" on a BF50A will get the blade edge too close to the lower unit" (not direct quotes, but close)
Thanks, FrankC

[secross2]

Thanks a bunch

[Frank C]

FrankC - Can you do the same thing for the Honda BF50A engine regarding prop selection and details that you did in this thread for the other engine?

opie, all I can do is look at Honda's website & repeat the basic specs for your Honda 50 ...

• WOT range is 5500 to 6000 rpms
• Gearing is 2.08:1
• Max prop is 12" diameter

None of this tells exactly which prop or what pitch will be best, for your specific loading of food/water/equipment. Your boat will undoubtedly need a prop pitch from 9 to 11 inches depending on those variables, but first you need to buy one and try it. If it gets into that "magic range" when wide-open, then it's good for general operations. Since you've never done this you might try to find a friendly dealer who can guide your testing - and provide some test props.

Guys who are very prop-saavy might later tweak their choice to improve some operating parameter - better economy, better planing, better for towing toys ... fine-tuning the blade profile or pitch to maximize in a narrow performance category. But that's fine-tuning.

But first, we all need to pin down the "gross-tuning" for our particular installation by trial 'n error. Buy a prop between 9 and 11 pitch & see how it performs. Most of us find some problem with the first prop test, like can't reach the upper rpms, or spins right past the upper rpms. Based on results, exchange for a different style or pitch and see if it cures the problem. Incidently, a "dog-eared" prop is another way to describe a "pontoon" prop.

Sorry, can't really help beyond that, except to suggest you PROBABLY should first try a 12-inch prop (approx diameter) with a pitch in the range from 9 to 11 inches (either of the last two props you cited). Choose a lower pitch if your boat is particularly heavy. Read all archived posts by Robert on the propping of 50-horse motors. Read them AGAIN, make notes, and try very hard to completely understand Robert's advice on various operating parameters of the smaller engines - you'll save lots of test time that way.