Need a little more speed

[IH8JEEP]

I have a 18'cc with a t-top with a 88hp motor. I would like a little more speed. Wife likes to go as fast. I know getting rid of weight will help. I don't want to remove the t-top because thats what we hold on to but would it be any help to remove the t-top canvas. My prop is a 13 3/4x15. I have a spare prop 13 1/4x17 that made the boat faster but only with a very lite load and takes a little to long to get on plane. I also have a fin on the motor is that helping or hurting top speed?

 

[smokeonthewater]

Re: Need a little more speed

the "fin" most likely won't help speed but the only way to know is remove it and try... pulling the canvas might gain you 1 or 2 mph but to make any noticeable increase you will need quite a bit more power... I'd say that a 150 should gain ya 15 mph or so.

 

[JB]

Re: Need a little more speed

Most 18' CCs are rated for 150HP, Jeep. The 70% rule of thumb says you need a minimum of 105HP for satisfactory performance. An 88HP, even with razor sharp rigging just won't hack it like 115HP or bigger would.

 

[IH8JEEP]

Re: Need a little more speed

Most 18' CCs are rated for 150HP, Jeep. The 70% rule of thumb says you need a minimum of 105HP for satisfactory performance. An 88HP, even with razor sharp rigging just won't hack it like 115HP or bigger would.

boat max is rated at 125hp
I will buy a reman. motor 125hp min but it will probably be a 150hp 99.99% when I do buy one.
This motor runs so good and trolls all day without a hiccup I just can't bring myself to change it yet.
Looking for about 5mph more. Boat runs now in the low 30mph on gps. Its a sailfish but the hull is a seacraft mold.

 

[tazrig]

Re: Need a little more speed

There are only so many things you can do to increase the speed. I would think losing the canvas would help a little as it may be acting like a "wing". Make sure your hull bottom is clean. You seem to be propped right so the only other thing I can think of is carry less fuel and loose any extra weight you can. If you get really desperate you could try ducking...:lol:

 

[saumon]

Re: Need a little more speed

You say the max is 125hp, so why would you want a 150hp? If you like the reliability of your 88spl, the OMC 120 look like the obvious choice...and I bet that 32 more hp will translate into more than 5mph!

 

[ondarvr]

Re: Need a little more speed

The fin may possibly help you to go faster, but you need to do some work to see if it will do anything. A fin will allow you to raise the motor higher on the transom, as you raise the motor the gearcase drag is reduced by having less of it in the water resulting in more spped. The fin is not supposed to drag in the water at speed, if it does it can slow you down and create odd handling. You will need to raise and lower the motor until you find the sweat spot where it performs the best, again, it may or may not help.

 

[smokeonthewater]

Re: Need a little more speed

loose any extra weight you can.

Sounds like Taz is saying she can go faster if she leaves you at the dock LOL


As mentioned above, motor height is worth a look... is your antivent plate an inch or so above the keel when parallel?

 

[UncleWillie]

Re: Need a little more speed

You say the max is 125hp, so why would you want a 150hp? ...and I bet that 32 more hp will translate into more than 5mph!

All things being equal... As in Larger motors do NOT weight any more....
Velocity is a factor of the Cube Root of the Power... Therefore....

88 hp = 30 mph (Given)
125hp = 33.7mph
150hp = 35.8mph
200hp = 39.4mph
300hp = 45.1mph

It takes a lot of power to get a little gain.


That said... the numbers do not look correct.
I have an 18 ft bow-rider with a 220hp I/O
It just barely makes 60mph on a good day, under ideal conditions, lightly loaded.
Working Backwards...

220 hp = 60mph (Given)
88 hp = 44.2 mph.

Something else may be wrong! :blue:
It appears you should be able to make 40mph without issue.

What does that Boat Weigh? Water logged?
What RPM are you getting at WOT?
Prop too deep?
Engine Trim adjusted?
Power may not be the problem.

 

[smokeonthewater]

Re: Need a little more speed

Keep in mind that old 88 is flywheel rated and equal to about 70 modern prop rated hp.

Also that CC is a really deep V and as such will be slower than a sofa boat with less deadrise.

 

[Mi duckdown]

Re: Need a little more speed

Jeep you got a good running motor. Don't mess with success, untill that motor craps out. although i would remove the whaletail and see what happens.!!

 

[Mischief Managed]

Re: Need a little more speed

If 88HP gets you to 30 MPH, 125HP will get you to 35.7, with the same weight, prop efficiency, and lower unit drag.

 

[Bob_VT]

Re: Need a little more speed

Your motor is prop rated HP (the rating system changed in 1984).......... the BEST solution is a different boat. The cost of even a re-manufactured motor with a bit more HP is probably still higher then a faster boat. There is your reason for a second boat or a different one.

So here is the conversation............Don't forget to smile!!

"Honey, we are going to satisfy your need for speed........ I am looking at a faster boat!"

 

[UncleWillie]

Re: Need a little more speed

If 88HP gets you to 30 MPH, 125HP will get you to 35.7, with the same weight, prop efficiency, and lower unit drag.

Actually only 33.7mph!
It is a function of the Cube not the Square. (Post #9).

And as you state, All things otherwise being equal...
Same weight, Efficiency, Drag, etc. Which we know will not be true.:cold:

Your results will vary... and murphy says, "Not for the better!"

 

[smokeonthewater]

Re: Need a little more speed

Your motor is prop rated HP (the rating system changed in 1984).........

WHOOPS! I thought those 88's were 70's models.... my bad.

 

[Mischief Managed]

Re: Need a little more speed

Actually only 33.7mph!
It is a function of the Cube not the Square. (Post #9).

And as you state, All things otherwise being equal...
Same weight, Efficiency, Drag, etc. Which we know will not be true.:cold:

Your results will vary... and murphy says, "Not for the better!"

You really think an 18 foot CC boat with a 300 HP outboard is only going to top out at 45 MPH?

 

[hungupthespikes]

Re: Need a little more speed

If the spare prop gets the speed your happy with, then a trip to the prop guy in your area may be the answer.
There's a prop section here on iboats you can go for some answers too.
Cupping, racking, going to a different manufacturer, SS vs aluminum, lots of options, IF your good with the speed of the 17 pitch spare.
If you want more speed than the spare prop can give you, then more HP maybe the only answer.

A good prop shop are truly artist and do some amazing things. They will let you try some options on your boat before you buy.

huts

 

[ezmobee]

Re: Need a little more speed

Well the good news is the performance you're getting is pretty much exactly what I would expect from that boat/motor combination so I think your motor is a good one and your hull isn't soggy. I wouldn't hang a 150 on it as that's stepping into V6 territory on a V4 rated boat but I certainly wouldn't have any qualms about hanging a 140 looper on it

 

[mpsyamaha]

Re: Need a little more speed

I would definitely try taking the fin off and seeing what happens. I dont think taking the ttop fabric off will be worthwhile, if you were in the 50+mph range then wind resistance would be more of a factor.

If it was me, I would start looking around for a 115-130hp motor, like said above you should stay with a v4 motor. I just put a 2001 yamaha 130hp on my 17ft deep v cc boat and it runs mid-high 40s on gps.

 

[IH8JEEP]

Re: Need a little more speed

Well the good news is the performance you're getting is pretty much exactly what I would expect from that boat/motor combination so I think your motor is a good one and your hull isn't soggy. I wouldn't hang a 150 on it as that's stepping into V6 territory on a V4 rated boat but I certainly wouldn't have any qualms about hanging a 140 looper on it

So a 140 looper would be a johnny/rude and be about the same weight I have now