Underpowered?

[alden135]

1990 Sunbird Cuddy 204 w/1990 Johnson 120hp:<br /><br />My engine seems to be performing very well however my boat takes quite a while to get on plane. Local marine mechanic tells me that my boat is severly underpowered. (my boat is not waterlogged) Any opinions?<br /><br />14x19 prop currently being used.

 

[vipzach]

Re: Underpowered?

Have you tried repropping the boat, or maybe some smart tabs?

 

[sangerwaker]

Re: Underpowered?

What is the boat rated for HP?

 

[JB]

Re: Underpowered?

You need a tach. Find out the rpm you are able to achieve at WOT. If it is not between 5,500 and 6,000rpm you have the wrong prop, are poorly rigged or both.<br /><br />Smart tabs might be a good idea, too.<br /><br />Good luck.

 

[alden135]

Re: Underpowered?

It's funny cause I went to the marina to purchase a stabilizer fin to help w/lift when the guy told me the boat was to big for it to help. I have a tach but have to do some work on it as I don't think it's working properly. The boat is rated for 175hp max but the 120 is what Sunbird (OMC) put on it. Once the boat gets up on plane it does fine, just takes a long time to get there.

 

[walleyehed]

Re: Underpowered?

A 150 would really be the minumum to expect much performance, and that includes hole-shot.....120 is a bit small for that rig, but you need to maximize it for set-up if you're gonna keep it.

 

[TELMANMN]

Re: Underpowered?

I have heard two different ways to figure out what the minimum for getting a boat up on plane. The first is 2/3rds the rated and the other is 3/4ths the rated. Using the 2/3 your 120 is at the minimum(117) while using 3/4 it would be a 131(proboboly 150 hp as I don't think anyone makes a 131?). <br /> From what I have seen usually the dealers want to keep costs down and will put the minimum package together.

 

[JB]

Re: Underpowered?

I don't think I agree, Kenny. <br /><br />I have found that ideally rigged and propped engines at 70% or more of rated HP usually give within 10% of max hp speed and performance. That is why I ran 70s on my Boston Whalers that were rated for 100hp. That cost me about 3mph at WOT (39.8mph).<br /><br />That 120 is within a small fraction of 70% of the rated 175.<br /><br />Of course, the Sunbird may be a slug of a barge but I would look first at the rigging and prop before I declared it underpowered.

 

[walleyehed]

Re: Underpowered?

I won't argue that on a BW, but the sunbird is heavy and hard to plane...<br />I also tend to think of applications at my altitude....if lower than about 85% of max, you have a slug.<br />At any rate, we agree that it needs to be set up properly to perform at it's max potential and that is the "Key" element when not dealing with the max rated power.

 

[TELMANMN]

Re: Underpowered?

Also how many people, how the boat is balanced with extra gear. I had a neighbor who would put 3 people in his aluminum fish/ski then put the cooler on the same side with the live well which was also the same side his gas tank and battery were on. He always complained it would lean to that side and take longer to plane out. By rearranging gas tank and cooler it would plane much quicker and straighter.

 

[mattttt25]

Re: Underpowered?

i owned a sunbird 20' center console. close to the same boat. ran a 150hp johnson. plenty of power, on plane very quickly without tabs or a foil. just didn't need them. boat also had a custom hardtop, so our weight was probably similar. yes, the 150 would be much better for you, but i agree with others you can make due with proper setup and proping. will also probably need tabs to improve your holeshot.

 

[alden135]

Re: Underpowered?

Thanks all for the info. I hope to de-slug my boat after getting the tach working right. I'll post back and maybe we can look into prop changes.

 

[cuzner]

Re: Underpowered?

Acouple of suggestions,move down to a smaller pitch prop, 17 or 15, and keep an eye on a working tach.And or instal tabs.If you have thousands to invest you can get a larger motor. If you can afford it a combo of a 17p prop and smart tabs should give you give you good hole shot, decent top end speed, and fuel economy.<br /><br /> Jim

 

[Jdeagro]

Re: Underpowered?

Alden;<br /><br />You have received some good advice here, and in my mind the first thing you should do is determine your WOT RPMs. This will determine if you are within the correct range as far as the prop is concerned.<br /><br />If you are the issue becomes one of "hull" performance. More than anything else, the hull (design) dictates the performance of the craft. As far as your dealer recommendation is concerned (under powered) his answer is classic, and typical of the common thinking in this country. The more HP the better! Gross HP is Good! <br /><br />AS I have said in previous posts this is not necessarily true and may very well be a gross error. Since our gas prices are low (keep in mind that our neighbors in Canada are paying about $3.50 per gallon and in the UK they are up to about $5.50 per gallon) we can afford to be HP hogs. <br /><br />After determining if the prop is in range, work with the hull. Add trim tabs! Trim tabs give you the ability to adjust the hull design as needed to make it more efficient over a more broad range of conditions. You will find that a few hundred $ will make a world of difference.