Raised my motor, but questions...

[McGillicuddy]

Capt Terry speaks truth.
1-1/4 " is fine. going up 1 more notch will probably be fine. 4-5 blade will help.

Other issues to consider:
1. What is your prop? Make/model (defines shape and what it was designed to do), diameter, and pitch.

2. What is your max RPM at WOT with a full load?

3. Another potential detriment is yer motor - if i'm not mistaken (and please correct me if i'm wrong) , its what Mercury sold as a 2+2 fishing motor. It was designed to save fuel at manatee zone speeds by firing 2 cyls, and then take off as the other 2 cyls fire as you reach high 2k rpm. means your low planing speed is compromised because that 2300-3200 rpm range is virtually non-existent. Thus your putting along or cruising over 20mph.

As Capt Terry noted 4 blade or 5 blade may help.

Post some answers and give the performance guys, something to work with.

Good luck. The 18 is a favorite among its owners and you should be happy!

[erebus]

It was a beautiful day today on Nantucket Sound, light winds out of the north, so pretty flat. Launched the boat and took her for a spin.



Right off the bat I noticed that she seemed to plane better. Faster.
Felt like I lost some of that drag-ass weight I've been towing around.

Produced 5000 RPMs max, with full throttle. The 2 stroke Merc 115 is indeed a 2+2 and the max rpm range is 4750-5250, so I'm bang on in the middle there.
Unfortunately my prop has absolutely no identifying characteristics whatsover. No stamps, no numbers, no nothin'. So I have no idea what I'm running which is frustrating. What was also frustrating is my garmin apparently lost its mind over the winter and couldnt find a single damn satellite. So speed is unknown, but it felt like somewhere between 27 and 32.

Flyingfrizzle is totally right that the handling is slightly different.
Noticed the sliding feeling in a sharp turn, but didn't bother me in the slightest.
Felt really smooth and controlled the whole time. God I love that Seacraft ride. Every spring I remember how smooth it is. Like riding in a nice creamy pudding. :-)

Otterhound, what were the specs on the cheap Apollo 4 blade you threw on there?
Now I need to start prop shopping.

[otterhound]

It was a 13 3/8 x 15 four blade Apollo and you may need a hub kit as well.
Rod

[Bushwacker]

Originally Posted by erebus

Unfortunately my prop has absolutely no identifying characteristics whatsover. No stamps, no numbers, no nothin'. So I have no idea what I'm running which is frustrating.

I bet if you take that prop to a good prop shop, they can figure out pitch and diameter, and maybe even assess how much cup it has in it, so that will give you a rough baselne to start from.

Did you happen to get any pics of the AV plate while you were up on plane? Now that you know it handles ok at the current height, I'd be inclined to raise it another hole to see if you can run even higher . . . might pick up another 50-100 rpm at WOT.

How heavily were you loaded today? When testing props, I always test with a full load of fuel, fill the galley seat water jug and live well, and fill my 65 and 70 qt coolers with sea water to simulate the max cruising load I expect to carry. Unless you don't ever run heavily loaded, you run the risk of picking a prop with too much pitch if you don't test with the max load you intend to carry! I'd also check min planing speed on every prop you try. I suspect that's real important for where you're running, because the 18-20' SeaCrafts are pretty light and will start going airborne at about 20 kts when seas get up around 3', so in those conditions, it's nice to be able to slow down and hang on plane at 12-15 mph, which you easily be able to do with that fairly light motor! Any 4B prop will have more stern lift than a 3B and improve low speed planning, and may be more efficient at cruising speed, although it may be a bit slower at WOT.

Merc has some good props, so once you know what you're running, you might contact Ken at Prop Gods, who seems to recommend mostly Merc props. Michigan also makes some very nice reasonably priced props, and their 2-piece hub system is more robust than the Merc Flo-Torque hubs, which have a reputation for shearing the plastic insert. Some PowerTech props also use the Michigan hub system. The 14 1/8 X 20P 4B Michigan Apollo was the first SS prop I tried and it was the most efficient prop I've ever tested, giving me a solid 5.0 mpg at cruise, and with a light load it also gave me 49.8 mph @ WOT, the highest speed I've ever seen! However I could only spin it up to about 5200 with a light load and only 4600 with a very heavy load (this is why I recommend testing @ max load!), and my optimum WOT rpm is 5300-5500, so I needed a lot less pitch!

[erebus]

So the boat was pretty much loaded as if I was going out for the day.
Full fuel (32 gals), but no food, beer or wife. And the bimini wasn't up. All the beach junk, anchors tools, etc. were stowed where they belong.

The AV plate was just visible beneath a scrim of water flowing over the top. The big stainless nut that holds the AV plate zinc was proud of the water flow.
I could probably raise it up another hole, but I think I'm going to stick with it where it is for this season.
Need to move it from my boatyard on Nantucket Sound up to its mooring in Cape Cod Bay in the next day or so.

I ran the merc prop selector tool real quick just now and its telling me I need either a 13x19 4 blade or 3 blade.?
I think the beater prop that's on there might be a 19 but I'm totally guessing. No real prop shops on the Cape. I'd have to send mine to Plymouth to have it checked out. Should've done it over the winter.
Oh well.

I emailed Ken at propgods and gave him the lowdown, and here's what he had to say (this was before I raised the motor):

I would suggest a Powertech 17 pitch NRS3.
If it hooks up well, and hopefully you can raise the motor and gain some speed. you'd be around 5100-5300 and that boat should run about 32 KTS, if that motor is strong.

So, now I have no idea what to do...

[Bigshrimpin]

Originally Posted by erebus

Right off the bat I noticed that she seemed to plane better. Faster.
Felt like I lost some of that drag-ass weight I've been towing around.

Flyingfrizzle is totally right that the handling is slightly different.
Noticed the sliding feeling in a sharp turn, but didn't bother me in the slightest.
Felt really smooth and controlled the whole time.

That's exactly how it's supposed to feel when you go from having the engine mounted too low to the correct height. I messed around with props on the 18 a little. IMO That hull likes a little bow lift and a smaller diameter prop so it can shake it azz around dancing across the waves. Too much stern lift on the 18 will get you wet and make the ride a bit harsh.

[otterhound]

Bigshrimpin's assessment is spot on IMO as that's how my 18 feels after adjustments and the 4 blade prop.
Rod

[76Red18]

Stock omc props have diameter/pitch stamped on the end of the hub. The prop nut washer hides the number. Maybe stock merc props are the same.

[CaptMick]

Erebus

On the numbers on the prop if it is older you may want to take a wire brush to the hub and clean off exhaust and corrosion. If that hasn't been suggested yet.

Also on the Garmin try mashing the Power and Page buttons at the same time as you turn it on. Hold them down until you get to accept or agree screen and that turns yellow. Then release the power and continue to hold the page button until it finds satellites.

I got that from the PO of my boat for the Garmin unit it came with and it works.

[erebus]

Originally Posted by CaptMick

Erebus

On the numbers on the prop if it is older you may want to take a wire brush to the hub and clean off exhaust and corrosion. If that hasn't been suggested yet.

Originally Posted by 76Red18

Stock omc props have diameter/pitch stamped on the end of the hub. The prop nut washer hides the number. Maybe stock merc props are the same.

I scoured the crap out of that prop. Threw it in the beadblaster, cleaned all the old paint off and looked in every nook and cranny.
No numbers... :-(