is prop size correct

[tyl]

I have a 17.5 aluminum sea nymph runabout with a 85 hp johnson 17p prop 2 people 32 mph gps and 5000 rpm. I do not have power tilt & trim. Would i go faster if I had tilt & trim? Or is this about as fast as I'm gonna go. This is the only boat I have ever owned.

 

[steelespike]

Re: is prop size correct

power trim does make it much easier to get the most out of your boat.
It gets you out of the hole faster lets you control the boats attitude on the water.makes it easier to control the ride in rough water
and make it easier to get the best high speed trim. And it does have the advantage of being able to raise the motor for beaching or running slowly in shallow or weedy water.
You can,if your patient, get things set well for the best speed and manually lower trim for better hole shot for water sports.
I do feel feel t&t is a good investment whether on a different motor or added to and existing motor.
Your basic setup needs to be right for the best performance.
Your anti vent plate(just above the prop) needs to be even with or slightly above the bottom of the transom.
Motor should be raised to a point just before venting becomes a problem.
Raising the motor alone could result in a couple of mph.I feel you might get into the upper 30s with some luck.
and careful trim and weight placement or removal.

 

[Texasmark]

Re: is prop size correct

Normally yes. Your rpms look good. Reason it helps is that the trim you use in the hole shot and running at lower speeds is less than the trim you run at WOT. I don't know the year of mfgr of your engine nor your prop material. Year is important in determining powerhead or prop hp rated and SS is a higher performing prop than Alum.

For a comparison between your boat and mine, my Avatar is a wake shot of my 17.5' Alum boat with a prop rated 90 Merc and a 24P SS prop running at 5600 rpm and just under 50 with 2 folks, fuel and gear. You would be amazed at how I can change speed and rpms with my trim button.

HTH,
Mark

 

[tyl]

Re: is prop size correct

the engine is a 1978 with a new ignition system and good compression. I have an aluminum prop. I have a 19p ss prop also but it takes forever to plane out when doing watersports.

 

[Texasmark]

Re: is prop size correct

the engine is a 1978 with a new ignition system and good compression. I have an aluminum prop. I have a 19p ss prop also but it takes forever to plane out when doing watersports.

Ok, you are powerhead rated so whack 10-15% off what your engine decal says. For that engine a 19 is a little high for water sports and any kind of load in the boat. You proved that by what you said about hole shot and toy problems.

HTH,
Mark