Another prop question

[Mechanicalmike08]

So I bought this boat at the end of last year and only got to use it 2-3 times. Then spent all winter rebuilding it. It's a 95 Larson 174sei, factory specs say 1800lbs. 3.0 with what I assume is the recommended 1.92 ratio gears. It currently has a 14.5"x19 3 blade aluminum quicksilver prop.

The few times I took it out last year and I just had it out for memorial day it seems to be lacking in top end. Barely over 30mph. I just switched to a GPS speedo. I unfortunately do not have wot rpms at the moment. We generally just run around, may pull a tube once in a while. 2-4 people usually.

I guess I'm curious if that seems like a common prop for this size boat, its looks really new and I'm curious if the previous owner just went and bought what he could. Also will say she seems to steer pretty lose at low speeds. Any help would be great.

 

[Sea Rider]

Without an installed tach and motor working topr won't see the light at the end of the tunnel any time soon. Motor's wot rpm achieved in flat calm water cond as usually loaded is a must know in order to play safely maximizing props. Any prop recommendation will be a theoretical wild guessing...

If boat was delivered with a prop it's a medium pitched one, doesn't mean that's right for your needs. WOT rpm is all, max speed achieved is secondary.

Happy Boating

 

[porscheguy]

Try the same model prop in a 21p.

 

[TunaFish389]

You need to verify top speed (with normal load) with GPS. And rpms which that top speed is achieved. Then figure out your drive ratio, they had a few 1 92, 1.98 or 2.0 for that year in 3.0 (could be wrong). I think you should be running 4600 to 4200 or maybe 4800 to 4400 in that year to me at full open. That is step one.. full open rpms and mph stats.

 

[jimmbo]

Gear ratio should be listed on the outdrive. On a Mercruiser, it will be on the Wraparound on the upper gear case, on a VP it will be on a metal plate. As mentioned earlier, without RPM information on current set up, it would be futile to say you need more or less pitch

 

[Sea Rider]

Try the same model prop in a 21p.

Without an installed tach, will be useless spending money trying a 21 pitch prop blindly, such prop will lessen actual wot revs achieved with current 19 prop, by how much ? will need to ask a nautical wizard....

Happy Boating

 

[harringtondav]

Same advice as above on getting a tach and understanding the engine's WOT rpm. Also (repeating) tuning the engine and pitching the prop for 4600-4800 WOT rpm is the objective. Overall performance will fall nicely in line after that.

BTW, I loved following your rebuild. This issue will be simple compared to that.

 

[Mechanicalmike08]

Gear ratio should be listed on the outdrive. On a Mercruiser, it will be on the Wraparound on the upper gear case, on a VP it will be on a metal plate. As mentioned earlier, without RPM information on current set up, it would be futile to say you need more or less pitch

The housing was stripped and repainted during my rebuild. I have the serial# but cant seem to find anywhere to look it up specifically for the gear ratio. Is my only option to turn over the engine and count the revolutions?

Weather isn't looking to good to get back out and get some real numbers.

 

[jimmbo]

A mercury dealer using the outdrive Serial #, might be able to pull that info from mercury

 

[TunaFish389]

This is what I found for the gear changes, its a blog so not sure the accuracy of the info.

https://www.perfprotech.com/blog/art...a2-sterndrives


"1991 thru 1995 – 0D469859 Thru 0F679999

1996 thru 1997 – 0F680000 Thru 0K999999

1998 and Up – 0L100040 And Up"

"What was a 1.98:1 thru 1995, in 1996 changed over to a 1.94:1

In 1998 Mercruiser introduced the 2.0:1 gear ratio to the Alpha Generation 2 Sterndrives which has since replaced the 1.94:1"

 

[TunaFish389]

Thinking about it, you should be getting 35+ mph on top with a 14.5x19p prop. My 14.5x17p (four blade) get 33 mph at top with an older 16.5' boat.

The 3.0 prop for the usual family boat normally run between 17p to 21p. In my opionion the 19p is most common.

 

[TunaFish389]

I think by the years we are both running 1.98 ratio. A side note the 1.94 to the 2.00 gear ratio is a one mph difference with the same prop. The 1.94 being one mph faster.

 

[TunaFish389]

Sorry to blow up your post but interesting that mercruiser only went with the 1.94 for three years. Then went to the 2.0.. Pretty sure it all had to do with price. The 1.98 was there for a decade. The pre alpha had 1.92. ..

 

[Mechanicalmike08]

I think by the years we are both running 1.98 ratio. A side note the 1.94 to the 2.00 gear ratio is a one mph difference with the same prop. The 1.94 being one mph faster.

Well according to my serial # (0F715316) I have a 96 outdrive in my 95 boat and must have the 1.94. It was a little rough when I was out as there were a lot of boats making waves so it was probably low anyway. Hopefully i can get back out on a calm day and see what she really has. I was mainly looking for someone to say the that prop was common for this size boat/motor and not just something off the shelf the previous owner threw on.

 

[TunaFish389]

Those boats won't effect you much.. I been out in 30 mph winds and yes they slowed me by a mph or two.

I think you got the right prop.. Just not getting to your max rpm. 44-4800 rpms. Figure out if your getting these RPM at top. Should bring you to 35 thru 40mph with current prop.

Data is so important for props. I would keep what you have till we get max rpm and speed.

 

[TunaFish389]

Even if you have the 1.94 it should be faster with the 19. Vs the 1.98

 

[harringtondav]

Also will say she seems to steer pretty lose at low speeds. Any help would be great.

My '96 SEI wanders at no wake speeds - a lot. Learned on this forum it's a curse of single prop, deeper Vee hull boats. I have to continually correct with the steering wheel from 10 o'clock to 2 o'clock. I have PS, and it's tight with very little play at the Teleflex steering rack.

Since you had your transom & gimbal assembly completely apart, I suspect everything is snug. A quick check is to jiggle the aft end of the drive side to side and observe free play. There shouldn't be any, or a 1/4" max. Loose clamping on the steering shaft at the tiller arm and at the gimbal ring are the usual culprits.

Per Bondo , it takes three sets of eyes to shake down steering looseness. One to jiggle the O/D, one to observe the transom plate and steering gear, another to observe and jiggle the steering wheel. I'm guessing you're just another victim of low speed steering wander/hunting.

Also for reference my 4.3, 1.81 180 hp Alpha II WOTs at 4800 rpm, 52 mph speedo with a 23P, 5200 rpm 48 mph speedo with a 21P but with better hole shot and cruising performance. My 174 SEI is speced. at 2400#. Maybe the V6 and PS account for the extra weight.

Again, getting your tach hooked up is the key to dialing in your prop. I love my Larson, but chop and waves beat me to death. 16'9" length doesn't smooth the ride much.

 

[QBhoy]

I’d say a 19” is common enough for that set up. But you are way down on speed. Presumably you are trimming out to get the top speed ? Sorry to ask. Makes a huge difference. I’d want to see an easy 40 mph gps from that set up, well trimmed and perhaps 2 onboard.

 

[Mechanicalmike08]

I’d say a 19” is common enough for that set up. But you are way down on speed. Presumably you are trimming out to get the top speed ? Sorry to ask. Makes a huge difference. I’d want to see an easy 40 mph gps from that set up, well trimmed and perhaps 2 onboard.

That's what I was hoping for, and yes i have been trimming to get top speed but might need to play a bit with it yet. Will have to see once I can get back out there. I'm hoping for some good weather here.