100hp on a 20 sf?

[Yz2009]

I've been reading a little on the 20 sf's. I'm considering buying a early 80's 20sf and have a few questions. I've seen some people saying 90-130 hp can be good for these hulls and was wondering is there any truth to that. I've currently got a seaox 2300 with a yamaha f100 and cruise at 22mph at 4700rpm and wot 28mph at 5400rpm. The hulls of the seaox and seacraft weigh about that same but the seacraft has a deeper v and is 3ft shorter. If I was to put the f100 on the seacraft would I get similar results? Also I've read 4s engines are not a good combination on these hulls but the f100 only weighs 366lbs and I could get rid of the oil tank and move the battery to the center console. Any insight would be greatly appreciated. Thanks.

[McGillicuddy]

Some would say you'll be underpowered, but you'll be fine. If you're satisfied with your Sea Ox numbers you'll be happy with that motor on the SeaCraft 20. Move everything forward like you mentioned and make sure the prop has some stern lifting qualities. Probably top out at 33mph and get excellent economy at low 20s mph cruise. Get some trim tabs or at least an SE foil to get on plane quicker.

I have a Seafari 20 with an '83 115 Merc and get 36 mph WOT and get out of the hole very quickly.

[seacraftks]

a 130 yamaha is all you need top speed with no trim tabs is 42 mph

[everybody]

What kind of #'s are people getting from the 140 suzuki's

[pair of jacks]

Interesting thread- I posted some months ago here that I was considering repowering with a 150 Yami 4stroke from my current 200 Opti- I received a lot of "don't do it" comments even though I think 150 hp is plenty for a 21 ft. SeaCraft- but the concensus here is that less is ok- why is that?

[seacraftks]

Hello I beleve its because there transoms are not redone a 150 yamaha would send your boat along around 55 plus Kts with great gas milage

[Bushwacker]

. . . but the concensus here is that less is ok- why is that?

The concensus is less WEIGHT is ok! Power can be whatever your wallet can afford! The 20' hulls were designed for motors that weighed ~ 300 lbs, so if you shift the CG way aft by hanging a 500 lb motor on the transom (or, even worse, move it further aft on a bracket) it WON'T RIDE like it's supposed to, and min planing speed will be in the low 20's instead of the low teens!

Most folks don't seem to realize how much more efficient the SeaCraft hull is compared to almost any other boat, so they don't NEED all the power you're used to seeing on other similarly sized boats. Carl Moesly got ~45 mph out of the early 21's (which are HUGE 21' boats) with just two 100 hp I-6 Mercs!

The 23's seem to run fine with a single 225, and the 20' hull will run fine with a light 85 hp motor. Ran mine for over 30 years with a 115 with no complaints, especially regarding the soft ride. In fact, the 20 will start to go airborne in seas over 3' above 20 kts, so if you run offshore a lot, you won't be using a lot of power. IMHO anything over 150 hp on the 20 is overkill! Maybe I'm spoiled because the E-Tec is a VERY strong 150 (actually 165 hp at prop), but I almost NEVER use all that power! The boat gets on plane easily at about 45% throttle (the I-Command gage displays throttle position sensor reading) and optimum cruise is about 37% with a very heavy Bahamas-cruising type load. Although it will run almost 50 with a light load, I rarely run more than 30-35 and generally cruise at 25-28 mph.

Another factor that reduces a SeaCraft's power requirement is the relatively light hull weight compared to other boats of similar strength. The early Moesly and Potter models were built like aircraft, with balsa cored soles and decks, with very tall and stiff stringers that were relatively thin but installed about half way through the layup and finally bonded to the inner liner, essentially creating 4 very stiff I-beams between the cockpit sole and the bottom. (Ask the guys who have pulled out the inner liner just how tough these boats are!) Hope this answers your question!

[Bigshrimpin]

SeaCraft- but the concensus here is that less is ok- why is that?

Fish - congrats . . . Now that you have reliable power . . . I'd forget about the kicker motor (until you have the bracket on) and just seal up the splashwell and splashwell gate as best you can. Trim Tabs will help a lot.

[Bigshrimpin]

Interesting thread- I posted some months ago here that I was considering repowering with a 150 Yami 4stroke from my current 200 Opti- I received a lot of "don't do it" comments even though I think 150 hp is plenty for a 21 ft. SeaCraft- but the concensus here is that less is ok- why is that?

Jacks your 21 is based on the 23. 150hp is NOT adequate power for your 2000 21 (23 - 2ft). 20's and newer Tracker 21's are very very different boats. FishS has a 20MA with a original 20" transom. It's got a wide transom with a wide open splashwell. He'll need to shed any extra stern weight to keep the transom above water. The 21/23 is a totally different story without any of the weight limitations FishS is facing here.

[Mark]

What kind of #'s are people getting from the 140 suzuki's

41mph at WOT with full 75 gallon tank in calm water, boat with t-top. 26-28mph at 4,000rpm, same load and conditions.