21' Starcraft aluminum cc - 115 hp or 140 hp?

matthewp

Petty Officer 2nd Class
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Jul 14, 2008
Messages
173
Hey folks.
I'm not posting this in the starcraft forum b/c I'm hoping for more views here. Thread title says it all. By the info posted on this site for Starcraft specs - the boat is rated for 140 hp. Anyone run a 140 on a similar hull? I have a few accounts of my boat running well with 115 - but I'm planning on adding some additional weight (t-top - mostly). Right now, I'm running the 75 hp Force ('97 model) that came on it. In a word.. DOG. I do know that Force rated hp at the powerhead, not the prop - so I don't even have the 75 hp in reality.

My first instinct is to hang as much hp as I can off the transom. It means more $ - but here is my thought process: having some hp in reserve is never a bad thing (long as I stay within manufacturer spec) - also, a larger engine not breathing as hard to maintain a set speed - say 35 mph - would be more efficient than a smaller engine at WOT to maintain the same.

I know this topic is well-discussed, and I have done some searching on this board already. Hoping for a little feedback on my particular situation. Thanks alot - and thanks for all of the great info on this site. Invaluable to me so far!

Matthew
 

Silvertip

Supreme Mariner
Joined
Sep 22, 2003
Messages
28,758
Re: 21' Starcraft aluminum cc - 115 hp or 140 hp?

The rule of thumb for power is to never power with an engine less than 75% of rated maximum. If 140 HP is the rated maximum, 75% of that is 105 so the boat should perform pretty well with a 115. Obviously there are times when the 140 would be nice but the cost difference may not be worth the difference in performance.
 

matthewp

Petty Officer 2nd Class
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Jul 14, 2008
Messages
173
Re: 21' Starcraft aluminum cc - 115 hp or 140 hp?

Thanks for info, Silvertip. I did come across that info in my previous search, and it certainly makes sense. It may just be the testosterone levels are spiking when I think about horsepower. My other thought is that I may not keep this boat forever (for all I know I might, though). If I did sink some money into a new, or at least newer, outboard, a 140 would hang well off a number of different boats, where a 115 would would limit my choices regarding new hulls. Thinking way too far ahead, I know. But hey, thinking ahead is free, at least.
 

tashasdaddy

Honorary Moderator Emeritus
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Nov 11, 2005
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51,019
Re: 21' Starcraft aluminum cc - 115 hp or 140 hp?

i'm with you hang the most you can. you don't have to use it. until you are outrunning a squall.
 

Tacklewasher

Lieutenant Commander
Joined
Sep 18, 2002
Messages
1,588
Re: 21' Starcraft aluminum cc - 115 hp or 140 hp?

What year is the boat?

I'm curious as my 1977 18' SuperSport is rated for 150 hp. It came to me with a 1977 70hp and I have an 1981 Evin 115 hanging there now. The 70 got on plane fine but maxed out around 28mph. the 115 takes it to 38, and I'm sure I can do better.

I'm guessing a newer hull based on prop rated hp. But I'm a bit surprised a 21' is rated for only 140.

I'd hang as much as you can afford on it.
 

matthewp

Petty Officer 2nd Class
Joined
Jul 14, 2008
Messages
173
Re: 21' Starcraft aluminum cc - 115 hp or 140 hp?

It's an '85 hull. If 115 takes your 18' to 38 mph, I'd expect slower results on my 21'. hmm. tips me toward 140 a bit more. Just ran out to the driveway to check the coast guard info plate on the hull. Sure enough - rated for 140. With my current outboard - I maybe make mid 20's for mph with another passenger and fishing gear. Granted, saltwater conditions rarely allow to run much past 30-35 in the first place - but for those flat calm days - hold-onto-your-hat fast would be nice.

I'm right with you on that thought, Tashasdaddy.
 

ezmobee

Supreme Mariner
Joined
Mar 26, 2007
Messages
23,767
Re: 21' Starcraft aluminum cc - 115 hp or 140 hp?

Yep, no one ever wished for less power :) My little Starcraft is maxed out at 85HP and it only hits speeds in the high 30's. Find yourself a deal on a 135 or 140.
 

Rancherlee

Chief Petty Officer
Joined
Jun 6, 2006
Messages
621
Re: 21' Starcraft aluminum cc - 115 hp or 140 hp?

My friend has a mid 80's 21' Starcraft fiberglass CC thats rated for a 150 and he has a late 80's 115hp crossflow Evinrude on his an with a T-top, 4-5 people on board, and fishing gear it struggles to get on plane (over 10 seconds) and only runs 34mph with this load. Before the heavy stainless steel T-top was installed and 2 people it got on plane in around 4-5 seconds and topped out just under 40mph.
 

triumphrick

Lieutenant Commander
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Jun 26, 2008
Messages
1,737
Re: 21' Starcraft aluminum cc - 115 hp or 140 hp?

Good post rancherlee. I have been experimenting with weight on my boat and what a difference a few hundred pounds make. I now don't take the second anchor with me unless I need to position my boat over some structure. Also, don't always run with a full 37 gals if I know I will be fishin the flats close in.

Some of those things we have been hearing about to increase fuel mileage in our cars can also help out here, as far as weight goes.

Seems as tho' I may be underpowered as well. Boat is rated for 150, but only has an 85. Planing takes about 6-8 seconds and burns about 5 gals/hr at 26-28 mph, so mileage isn't that bad. Something I can live with for now.
 

Silvertip

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Sep 22, 2003
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Re: 21' Starcraft aluminum cc - 115 hp or 140 hp?

Just a word about selecting an engine for "this" boat because you may use it on the "next" boat. That logic may sound ok but your next boat will likely be much newer and your engine just that much older. I've sold lots of boats over the years, with and without engines. The engine makes the boat, so selling a boat sans engine does not sell as quickly or for as much as you would think. That's not to say you won't get lucky, but most people do not have the knowledge to install an engine so they would need to have someone do it for them which only adds to the cost of the boat. So my feelings are, put the engine you want on it, and let it go with the boat. If you buy a new boat, it will likely be properly powered with a newer engine. If you don't like that combination but like the boat, you can always sell the engine since there is a good market for them. Then put whatever you want on it.
 

matthewp

Petty Officer 2nd Class
Joined
Jul 14, 2008
Messages
173
Re: 21' Starcraft aluminum cc - 115 hp or 140 hp?

My dad has a friend with the same hull I've got. He runs a 115 on his and Dad tells me it rips along pretty well. This guy's boat is pretty stripped down and light, though. I'm planning to add more fuel capacity; currently an 18 gallon below deck tank and a spare 6 gallon above deck tank is what I've got - like to have at least twice that. Add to that the t-top, a full day's worth of ocean-going gear for two to three guys, water, food, and more tackle than I have any business owning going in the boat too, and 140 hp is the number that keeps coming to mind.

Silvertip, I do agree that shopping for a motor that may hang off a newer boat in the undetermined future is probably not the best strategy. With more time than money (actually, both are in short supply at the moment), I tend to overthink every little thing. With the weather being majorly uncooperative here in the northeast for pretty much the whole month of July, I've been doing way more ruminating than running!
 

clanton

Rear Admiral
Joined
Jul 9, 2001
Messages
4,876
Re: 21' Starcraft aluminum cc - 115 hp or 140 hp?

140 cross flow Evinrude/Johnson if you can find one. Light weight, and plenty of power. The 1978 bow rider rated for 150.
 

Supersport18

Cadet
Joined
May 8, 2008
Messages
20
Re: 21' Starcraft aluminum cc - 115 hp or 140 hp?

I have a 1975 Mariner CC pretty much like yours. I've just re-built the transom and will be putting the 125 Chrysler that came with the boat back on. But I've been tossing around the idea of using the 55 johnson and finding a second one of the same vintage and running twins. Anyone have any experience as to whether or not It would get the same performance as a larger (single) motor ? Or would there be more drag and weight?
 
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