100hp on a 20 sf?
 

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.

Re: 100hp on a 20 sf?
 

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.

Re: 100hp on a 20 sf?
 

I have a '72 Seafari 20', '06 Mercury 90 hp Optimax with 13.25"X21P 4 blade and skeg-mounted Hydro-shield. WOT 33-34 mph, cruise 24 mph at 5.1 mpg. Planes quickly.

Remember, the most common original equipment motors on these 20' SeaCrafts were the 85 hp and 115 hp V4 Evinrude/Johnsons, or the 90 hp or 115 hp inline 6 cylinder Mercury motors. As a SeaCraft dealer, I have even rigged a 20 SeaCraft with a single 70 hp motor, and it did fine. There is also another member with a 20' Seafari rigged with a Mercury 80/85 hp two-stroke 4 cylinder. These hulls don't need all that extra horsepower.

But if you want to put the extra power on, they'll handle it just fine. Locally, there's a 20' 1971 SeaCraft Superfisherman with a Porta-Bracket and a 250 Yamaha HPDI that runs like a raped ape. (Of course, he only averages 2.5 miles per gallon.) :D

Re: 100hp on a 20 sf?
 

This is a good thread to read. I was wondering about a Honda BF90 on a bracket on a 1971 SF20. The bracket is aluminum, but i will foam fill it. A honda BF90 is 370lbs more or less. I don't need more than 30 knots, and a bit less is fine.

Re: 100hp on a 20 sf?
 

No need to foam fill the bracket if its already a closed hollow chamber. If you don't already have the Honda you might consider an Etec 90 for your application. You will cut the weight by 50 lbs and get every bit the of the 4 stroke economy.

Re: 100hp on a 20 sf?
 

I don't know anything about the etecs. I know I love my other Honda because it ALWAYS starts. The economy is nice as is the lack of two stroke fog.

I was even thinking dual 50s and no kicker with a flotation bracket. I have no motor yet. Heavy, but lighter than a motor and kicker.

Re: 100hp on a 20 sf?
 

If you're thinking twin 50's, think twin 60's by Honda or Evinrude, instead. The weight and fuel consumption is similar, and the power is 20% greater.

Re: 100hp on a 20 sf?
 

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

Re: 100hp on a 20 sf?
 

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

Re: 100hp on a 20 sf?
 

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?

Re: 100hp on a 20 sf?
 

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

Re: 100hp on a 20 sf?
 

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!

Re: 100hp on a 20 sf?
 

I have rigged new 20' Seacrafts with only 70 hp, and they did just fine. 85/90 hp and 115 hp motors were the standard. The original hull is designed for 300 lbs OR LESS !!

Re: 100hp on a 20 sf?
 

IMHO opinion 150 is perfect - less weight the better, 4S is just usually too much except the zuke 140. Will a 130 work sure, will a 100 get it on plane ya, doesn't mean the boat works as well at planing speeds. Its not all about WOT, the extra power makes the boat work better at low speeds and cruise. Getting the hull to ride higher on the deeper vee is what its all about - low HP will not do that, they slog like everything else, not why you buy a SeaCraft. It is a high performance hull and needs X amount of HP to work as designed - just say'in.

Re: 100hp on a 20 sf?
 

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

Re: 100hp on a 20 sf?
 

The "ESD" is correct.....It's not all WOT. It's how it performs with a load of people, tackle, fuel, coolers, ice, etc. Does it get on plane properly?? Run well in all sea conditions, even emergencies?? Provide optimal fuel mileage with little strain on the engine at cruise??

I've been at WOT once, however was not able to catch a single fish.

Re: 100hp on a 20 sf?
 

I caught a fish at WOT once. Dam..d flying fish flew out of the water and smacked me right in the chest. Actually I didn't catch it, it bounced off and landed on the deck. :D

Re: 100hp on a 20 sf?
 

Any opinions on the Yamaha F100? There are a few available on Craigslist used. And ther are 356 lb.

Looking for modest reliable performance. 4 stroke is a must.

Re: 100hp on a 20 sf?
 

Ive got a 99' F100 and its a great motor. Only thing is dont let gas sit for a long time in the carbs or it will get gummed up and they will have to be cleaned. The only issue ive ever had with it, is the voltage regulator went bad last season. So 11 year old motor and only issue to date was a voltage regulator. Always starts first crank as long as youve got good gas.

Re: 100hp on a 20 sf?
 

You just described SUZUKI

Re: 100hp on a 20 sf?
 

Re: 100hp on a 20 sf?
 

I just bought a F100 for my 20 M.A.

What prop do you run, and do you run a fin? A new prop is in the budget.

Re: 100hp on a 20 sf?
 

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.

Re: 100hp on a 20 sf?
 

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.

Re: 100hp on a 20 sf?
 

I thought the hull shape on those newer Tracker 21' looked different than the original SC 20's. The leading edge looked more like a 23'. Glad you confirmed that. I guess the Tracker 21' was a hybrid between the Potter 23' and the Moesly 21'.

Re: 100hp on a 20 sf?
 

The new 2000 (or whenever they were introduced) and newer tracker 21's are based on the 23 . . . not the 20hull. It's essentially a short 23 hull.

Re: 100hp on a 20 sf?
 

I have a 2003 21' with a 200 Merc EFI. I know I wouldn't want any less HP. I would love to have a 225 on mine. I had a 1969 20' with a 140 on it and it was a good match. There's a lot of difference in the two boats.

Re: 100hp on a 20 sf?
 

any opinions on a prop?