What style prop do we like on a 20' Sceptre
 

Its time for a prop. This one is old, dinged up, and just tired. I want a new shiny stainless one. I'll keep this as a back up to get me home in a situation.

My setup is a 77 20' Sceptre with 2005 Optimax 175 on the transom. Its a 19pitch aluminum prop. RPMS seem fine. Cruising at 38mph at 5k rpms with more to go. I've adjusted motor height to where it should be. Plate visible at cruise.

The question is do we like 4 blade or 3 blade props for this boat? I know the typical ins and outs of a 4 blade vs 3, but I thought maybe there were more things to consider when its on a Sceptre, due to its different weight setup.

What I do notice now is it blows out easy in tight turns, or even when trying to accelerate after a quick drop off plane. But mostly turns. I don't think it was like that until I brought it up 2 holes. The plate was well below the water on plane before though.

The use of the boat is as a utility to carry stuff to and from the island house. We also fish a lot in the bay, and probably will venture out a bit to open water, but rarely. The bay can get ugly so a slow plane speed would be preferred. Obviously I have a 175 so I want to go fast too!

Suggestions?

Drop it one hole and stay with a three blade.

Leave the motor where it is as a new stainless prop will have better cupping and grip. I would choose a Mercury prop. They make some of the best props on the market and are used on all manufacturers.

If you are going with a 4 blade, I would go with either a 17 pitch Rev 4 or Vensura

Most big mercury dealers have loners or will let you try a prop. You can also contact Ken @ prop gods and get good advice.

For handling and utility absolutely try the 4-blade first. Drop 2-3 inches of pitch from current 3-blade. For the Opti I suggest the Rev4. You may still have to drop the motor one hole, but I'd try the 4-blade with it's increased stern-lift first.

Good info. I'll be stopping in to the dealer tomorrow to see if they have a Rev4 in 17p for me. I'll report back once I get to try it out. Plus I'll have my Smartcraft tach so I can really see if I'm at the right RPM too.

A couple of years ago I talked to Ken at Propgods about blowout on tight turns when the drive is high - If I remember correctly, he said that a little bit of cup on the tips will fix it without having to change height.

Prop Cupping
 

When I picked up my new Seafari in 1976 from Brown & Hauptner, Mark Hauptner who had raced for Moesly added a cup to my Merc prop. Not sure how common cupping was at the time. Didn’t find out until I met Carla a few years ago that Frank Brown was Moesly’s race mechanic. Explains why my SeaCraft was set up so well!

I remember Frank Brown well. In the early 80's, I used to manage Waterway Marina in Palm Beach Gardens at PGA Blvd and the Intercoastal. Frank Brown's Marine was 150 feet away across the highway. Frank Brown did the setup and tuning on two of my boats, including my first SeaCraft, a '70 Seafari that my uncle had bought new from him.
He advised me on my repower, going with a Merc 1500XS powerhead mounted to regular 20" mid. That boat had the transom cut-out for twin motors, I remember.

I used to go over and pick his brains on everything from props, to trim, to hull design. He had more stories and anecdotes... I used to listen to stories of famous people like Carl Moesly and the bone-headed stuff they would do. Made me realize that I was just as bone-headed as they were. He's the one who got me started in offshore racing at Gulf Wind Marine as a throttleman.

The other setup setup he ever did for me was with a '73 Merc 150 inline 6 on a '73 Slickcraft SS160 turning a solid 2 blade 24p bronze cleaver prop. He added two small 6" wide hand-adjustable trim tabs just outside the keel-line that took the boat from squirrelly at anything over 50 mph, to rock-solid stable at 70+. I could just touch 72 mph with that boat at 8800 rpms. He estimated that at that rpm the motor was actually producing 170-175 hp.

Here we go. Rev 4 17 pitch. Going to try it out tomorrow!

and how did you like the rev 4?

I wasn’t too fond of Frank initially. I did most of my original boat purchase and other things through Hauptner. Frank was kind of crochity or something, but got friendlier after they split and I bought my second Merc. I remember Frank showing me the first Oceanmaster or its predecessor when they were still together on PGA. The father of a friend bought the first or second one, which I didn’t find out about until I rode in it a few years later when he gave it to his son, Phil. On a real rough day was glad to follow in his wake from Jupiter to PB inlet.

It was great! Just got back last night from a weekend of boating with it. Quick to plane, no blowouts. Got to 5400 rpm at 43mph with 2 people, 2 large dogs, a completely full gas tank and a boat full of gear/food for 3 days.

I'm thinking maybe the motor might want to come up another notch. When I got the boat it was at the bottom. After watching the plate, I brought it up 2. With this prop, I am able to hit the trim limit without sucking air. It jumps up and rides nice and high, but maybe there is more? I did not get a chance to watch the vent plate this time, so before I move I'll do that. I was keeping an eye on water pressure though, and it never faltered. Should I be able to vent the prop?

Overall very happy with the way this boat rides now. I'll have to let Ken@propgods know. Thanks for the recommendation, guys.

I done a little mercury prop testing with my 20 sceptre and it ran well with the 17 rev 4, not the fastest but best plane speed and really helped on the blow out you talk of. I have my motor up high and experience the same with the 3 blade smaller dia props. The rev-4 will run an inch or two higher than most and still be happy. The mirage 17 with raise the rpms up over the rev 4 17p prop and a mirage 19p will fall about the same rpm as the rev-4 17p. You don't get the same cupping power as the rev 4 simi-surfacing prop with the mirage but it still dose very well for a 3 blade. You will see a few mph fall off the low plane speed though with it. I currently have a 21p 14.5 dia quick silver vengeance a41 on there currently. Not much cup and it dose blow out a fair amount more. Low plane sucks but it is 4-5 mph faster on the top end than the rev 4. If I go out in the ocean or ruff conditions I throw the rev 4 on her. If I am in the creek on a slick day like most fishing days I run the light weight thin bladed a41 vengeance. The 19p mirage seems the be the best all around prop for anything you throw at it. I have the older mirage a41 17p and the newer a45 mirage plus with the ventilation holes. You can tell a difference between them as well even with the holes pluged. The older a41 props are thinner bladed and faster but do flex more. The newer ones seem better on the low end and have more cup or grip.