Engine Revving!

[keeper]

Hi

I Have A 1977 17' Terry Bass Boat W/ A 1977 175 Hp. 14.25 Dia X 25 Pitch Sst 3 Blade Hooter Prop.
Anti Vent Plate Even With Bottom Of Boat. Wot Is 47 Mph At 5k Rpm. This Is My First Boat, And I Have Never Been In Another Planing Craft. Heres The Problem! When I Go To Get On Plane I Put Pedal To The Floor, If I Don't Engine Will Bog Down And Want To Stall, Bow Climbs, And At Around 2500-3000 Rpm It Almost Seems Like The Prop Loses Bite And Starts Spinning Up To 5800, Then After 5-6 Seconds And A Lot Of Over Revving I Am On Plane And Everthing Is Fine, Except I Can't Get Over 5k Rpms. Heres What I Have Been Told!

Spun Hub! But If I Had A Spun Hub Would I Be Able To Do 47 Mph.

Heavy Boat! So I Took Out Floor And Removed Wet Foam, Only A Couple Hundred Pounds.

Over Propped! Is This What A Boat Acts Like When Overpropped.

Also With A 17' Boat And 175hp Shouldn't I Get More Than 47 Mph.

Any Help Would Be Greatly Appreciated.

Thanks

Mark

[vector mike]

It sounds like the prop is cavatating when taking off and the lower unit is too deep to get the revs up on top end.
Get some cup put into the prop and lift your lower unit up. That should help on both ends.

[tdogcarter]

Mark,

First off if you had a spun hub you would not be able to even go at all, any spun hub I had does not do any more than idle speed since the rubber is no longer in contact with the hub.

Second you probably do not have the right amount of pitch. No clue where your at or where you run, but what I would start with is a 21 or 23 trophy prop and see what you get for RPM, these are GREAT all around props and work on most anything. You can get them used or on here for around 200 – 250 for a good prop. You should be seeing RPM in the 6K range for that engine.

Also what your getting when your engine revs up like that is called Cavitation and is not a bad thing, but yours seems to be kind of higher on the RPM than most. I am assuming you have a Shooter prop and not a Hooter prop. Hooters has a nice boat, but they don’t make props that I am aware of.

Do you have a jackplate so you can easily and quickly adjust engine height? Do you have dual cable steering on your boat?

I will say normally a 17’ boat with a true 175 hp will do over 47 mph, the 77 engines were rated at the powerhead so your probably closer to 150 hp. Either way you should see 60 with the right prop.

Trey

[keeper]

Hi Guys!

Thanks For All The Info! I Do Have A Manual Jack Plate And Dual Cable Steering. My Prop Says Hooter On It. No Other Numbers Or Letters Anywhere. I Think They Are Worn Off. I Will Try A 21 Or 23 P Trophy. 3 Blade Or 4? I Work In A Machine Shop And Took My Prop In And Put It On An Indexing Head With An Indicator On The Blade, Moved 1 Degree And Multiply Reading By 360 To Get Pitch. I Came Up With 25 In.

Thanks Again

Mark

[Dean Dorsey]

I would just like to add a couple of things. I don't believe for a moment this is your top end problem, but a prop rubber hub can be partially spun if you will. My parents own a 21 chaparel sport I/O hull the hub will spin comming out of the hole to the point of almost not making it on to plane. Once finally on plane and the load is reduced it no longer spins. Kept thinking it would totally go and he would finally have to get it re-hubbed or get a solid hub. For 2 seasons now he has left it this way and it has not gotten worse. So you can have a partially spun rubber hub. Next have you determined you have a healthy motor? Compression check, leak down, or even that you are getting cosistant and correct spark and fuel on the top. Are the cables adjusted correctly, butterflies opening fully, fuel pump working properly, any obstructions between tank and motor, have you looked at timing. After those things have been established, and assuming that prop depth is not your problem I would look at the condition, pitch and possibly even the style and diameter of the prop.
I would start with a compression check, and move on to spark. Ground plugs on block and test at all throttle ranges and make sure all are at least firing at home. It could be any of alot of things, approach 1 at a time to eliminate each source as the problem then move on to the next.
Case in point I own a 21 skater with a modified PM 300 that will only run a top end of 91 GPS, at around 5,800 rpms. This motor has Simon heads, SVS intake and all the other bells and whistles to make it go faster. I know the top end for this setup in stock form should be 96-100 and about 104 for this setup. The motor exibited some other small problems but nothing that pointed a finger at any one thing. I did a simple compression test and found that all bores were between 108 and 112 and that was with tighter heads, when they should be around 135 with heads. Not to say new rings and maybe pistons will solve all my problems, but I know where at least 5-7 mph on top have gone. I can prop to high heaven but it will not bring the speed up to normal with a motor that is making 15 to 20% less power than it should be when healthy and my current rpms at 5,800 with 30 pitch prop is at least in the low end of normal for the power range, but if I were only turning 5000 I would on a temp basis change my pitch to get into the proper WOT power range. Properly working tach is a good diagnostic tool. If it is jumping around first check for good connections especially grounds, then look at the rectifier. DD

[keeper]

boy, do you guys know your stuff. i guess i have a lot to learn. that sounds good making sure motor is healthy,it is a 1977. so i guess i have some work to do. thanks
for all your help.

mark