Picking The Right Boat Prop

[Cracken0812]

I have a 1978 150 Johnson that runs strong as it could be. When i bought the boat, it came with the 19 pitch 3 bladed prop that I am currently using. I was curious to get some opinions on what the right pitch of prop I should use on this older motor? I have a 86 Ranger with the 78 150. I'm not looking for a speed boat by any means but I wouldn't mind gaining a little speed without hurting my engine. Its a project boat but hey I have to start somewhere. I don't want to push my limits on over working the motor. Thanks!

[sixstring531]

I am by no means an expert, but from what I understand you want a prop that maintains, or is lower than, your engine manufacturers recommended wide open throttle (WOT) rpm when wide open. I know everyone has a preference - hole shot vs top speed - but as a fisherman with not a lot of money, I try to maintain the motor the way the manufacturer suggests.

Right now we're in a 99 ProTeam 185 with a merc 75. The recommended WOT is 5200rpm (or around there) and the prop is a 3-blade stainless steel 13x21, which is two inches larger than the stock 13x19 merc has on their 75. It has an excellent hole shot and can run 40+ just under WOT. This is acceptable to me. I think the rule of thumb on pitch is every inch is 200 rpm...(or something like this) Someone else can speak up and correct me here.

[REDSOXWSCHAMP]

SMALLER PITCH SIZE = MORE RPM'S

[J-Doc]

Having a motor of this era and manufacture type, you need to be able to achieve at least 5,000 rpm or you are bogging the motor and that's not good. I believe 5,500 is the max recommended rpm range. My manual states it's not reaching maximum horsepower until 5,000 rpm.

I suggest you contact fishinwrench and provide some detailed specifics. This era of outboards is his bread and butter.

[J-Doc]

What speed are you getting with the 19? Rpm? I run a 19 3-blade on my 85hp Rude and switched to a 17 with more cup to get less prop slip (can't lower my motor any more so this was best option). Surprised to read you have a 19 currently. I would have guessed 21 at least.

[fishinwrench]

I would expect it to leap out of the hole....but wind up a bit too tight with a 19p.

You should be able to turn a 21p 3-blade with that setup and keep her just under 5500 loaded.

[J-Doc]

I would expect it to leap out of the hole....but wind up a bit too tight with a 19p.

You should be able to turn a 21p 3-blade with that setup and keep her just under 5500 loaded.

My thoughts exactly. Just less wordy. LOL

[Cracken0812]

Thanks for everyone's reply. The max rpms I've got it to was 4500 and 42 mph. I do have a hydrostabilizer on it as well so definitely do not have any problems getting out of the hole. I think I have a shift linkage issue as well that I why I can only get it to 4500 rpm, but at the same time it's a old motor and I don't care to push it to the max. I will try finding a 21 pitch that doesn't cost me a arm and a leg. Like I said it's a project boat but I don't mind spending a little to gain some speed. I plan on leaving the stabilizer on because I've been in plenty of Rangers that are heavyyyy boats like mine and know it takes a bit to get out of the hole. I know this will cut down on some of my top end but it beats not getting out of the hole quickly.

[fishinwrench]

You're not gonna gain anything with a 21 if you're only turning a 19p @4500

I think you might have a sync/timing issue.

[Champ188]

Something doesn't sound right in the setup. If this is an 18-foot Ranger (one of the 300-series boats such as the 350, 360 or 370), that 150 should be turning at least 5200 with a 23 or 24 pitch prop.