Mercruiser 4.3L pushes 2400# runabout only 36mph max

[Seaduction19]

The Boat: 1993 Marada Armada 1800MVB roughly 2400 pounds
This year engine was replaced with remanufactured 4.3l 2bbl TKS (190) mercruiser.
Alpha1 gen2 drive, gear ratio 1.81 with HighFive 19P prop
The boat seems to run really well but I feel it’s too slow for what it is. At WOT and planed out, my Lowrance GPS/Fishfinder tells me I’m only going about 34-37 mph just me with a full tank of gas (28 gallons) onboard. I believe I remember the rpms being pretty close to the 4400-4800 but can’t be sure and unfortunately everything is iced over so I can’t check. All this was either on glass smooth water or slightly choppy water. I do not use trim tabs or a hydrofoil. Does anyone have any input to why I might be going so slow?

 

[alldodge]

Using your numbers tells me the only reason your reaching 4400 and above rpm is because the prop is ventilating. I'm seeing 15 to 20 sum % slip and that boat is so light it shouldn't happen.

So many folks slap on a 5 blade prop and actually loose performance. The boat probably came with a 21-3Blade and a 19-5Blade is about like 22 or so

I would find a 3Blade 21 and see what it does come spring

 

[Seaduction19]

I have literally been stuck on the prop as the problem for days now. After all my research I figured that it has to be that stupid 5 blade but then after sitting on it, I figured, would a 3 blade laser2 21p really give me 15mph more? 52mph seems to be everyone else’s average speed! I’m still going to absolutely switch the prop but I’m just not expecting magic. Your advice is very much comforting and appreciated as to that’s where my heads been at too.

 

[alldodge]

Use the prop slip calculator and plug in numbers to see what may happen. Note this is what "may" happen. I entered your info and left out the speed at WOT. Using 10% slip it calculates the WOT to 47.46 mph

10% is nominal and the boat should get less in the 7% area all trimmed correctly. Enter your own info and change things to see how one thing effects the other

Enter 21P, 1.81 ratio, 4800 rpm, 10 % slip, then select speed
http://bblades.com/propeller-slip-calculator/

Do note I'm using the 21P prop, if I changed the slip to 5% then top speed increases to 50 mph. Many folks on the net post speed using the boats speedometer which is not accurate

 

[Scott Danforth]

you sure your boat is weighing in at 2400? did you put it on a scale?

are you trimming out the drive?

dry weight on your boat is 2260, not including fuel or you. full of fuel and you and you are pushing 2620 and that is assuming no gear.

 

[Scott06]

If you haven’t run it with a different prop, I’d second trying another prop. I tried a high five this past summer and got similar results, lots of rpm and boat didn’t go anywhere.

 

[vroom ZOOM]

I have literally been stuck on the prop as the problem for days now. After all my research I figured that it has to be that stupid 5 blade but then after sitting on it, I figured, would a 3 blade laser2 21p really give me 15mph more? 52mph seems to be everyone else’s average speed! I’m still going to absolutely switch the prop but I’m just not expecting magic. Your advice is very much comforting and appreciated as to that’s where my heads been at too.

laser better for high end speed. could also try an enertia. If you are on a budget and want good speed then people have been seeing very low slip and good performance with the solas scorpion. the only thing is that the scorpions run "stiff" so a 19p runs like a 21p.
5 blade is for tubing or wakeboarding. try merc prop finder and see what they offer. also find a prop shop and plug away at a few props.

 

[Rick Stephens]

I've got a 2800 pound v hull that with a plain jane 4.3L Vortec and an el cheapo 21 pitch 4 blade Solas that I get right up to touch 48 MPH at 4800 RPM. If I stuck a 3 blade that was properly chosen for top speed I'd bet 51 or 52 MPH. I never run up there, so I don't care much My cruise is 36 MPH at 3600 RPM. You should be very similar. I do run Smart Tabs, but at top speed they add drag, and are not a benefit. I trim up till I have the least hull in the water. I think you need to prop better.

 

[Seaduction19]

Use the prop slip calculator and plug in numbers to see what may happen. Note this is what "may" happen. I entered your info and left out the speed at WOT. Using 10% slip it calculates the WOT to 47.46 mph

10% is nominal and the boat should get less in the 7% area all trimmed correctly. Enter your own info and change things to see how one thing effects the other

Enter 21P, 1.81 ratio, 4800 rpm, 10 % slip, then select speed
http://bblades.com/propeller-slip-calculator/

Do note I'm using the 21P prop, if I changed the slip to 5% then top speed increases to 50 mph. Many folks on the net post speed using the boats speedometer which is not accurate

That was a great tool. I do really find it helpful to find the theoretical speed and using it just irritates me more that I can’t go see for sure what my RPMs were. I do stand with it being around the 4800 though.

 

[Seaduction19]

you sure your boat is weighing in at 2400? did you put it on a scale?

are you trimming out the drive?

dry weight on your boat is 2260, not including fuel or you. full of fuel and you and you are pushing 2620 and that is assuming no gear.

Yes, so I did attach a video to my opening thread. In that video I do have very limited gear. Maybe 100lbs between all required safety gear and a lighter tackle box and fishing pole. I do have a full tank of gas and I’m near 220lbs myself. I do trim correctly and anticipating that question is mainly why I posted the video lol.

 

[Seaduction19]

If you haven’t run it with a different prop, I’d second trying another prop. I tried a high five this past summer and got similar results, lots of rpm and boat didn’t go anywhere.

That’s good to hear! Makes me feel more confident that that’s the issue.

 

[Seaduction19]

I've got a 2800 pound v hull that with a plain jane 4.3L Vortec and an el cheapo 21 pitch 4 blade Solas that I get right up to touch 48 MPH at 4800 RPM. If I stuck a 3 blade that was properly chosen for top speed I'd bet 51 or 52 MPH. I never run up there, so I don't care much My cruise is 36 MPH at 3600 RPM. You should be very similar. I do run Smart Tabs, but at top speed they add drag, and are not a benefit. I trim up till I have the least hull in the water. I think you need to prop better.

I would be very happy to get numbers like that. its not necessarily that I even want to gain more speed but the numbers and science tell me that there is in fact something wrong with my boat. Its just odd to me that I am finding posts out there where guys have a 20' runabout with a dry weight of 2900# and are pushing 50mph using the exact same drive train as me minus the prop. I can't even get 38mph.

 

[Scott06]

That’s good to hear! Makes me feel more confident that that’s the issue.

Yeah the high five was totally disappointing. I had for fun and knowledge base been trying several props over the years. high five was the last one, basically my test order was set by when I found them used on eBay...still have my best results with a revolution 4, enertia was a close second.

If you want to try something less expensive to rough in the pitch I had excellent results with Michigan vortex 4 blade props on my old boat (searay 170/3.0 engine). they make both 3&4 blade, depending on your use. For loaded watersports I generally run 4 blades.

 

[QBhoy]

Hi 5 will always lose you speed and can sometimes act like an inch less pitch from a 3 blade of the same pitch. Lots of prop slip near the top end of things too usually.
from thinking of many boats similar with 4.3 and that ratio. I’d be pretty sure you are underpropped at a 19” there. The best of results from similar boats and lower would be towards the 50mph mark at best and a fastish hull. Mid 40’s loaded and most times would be the norm I’d think. I’d go to a 21” 3 blade or even a good big diameter 3 blade 19” like a tempest would have you running much much quicker for sure.
Only fit a foil fin, if you want to lose more speed...haha.

 

[Seaduction19]

That’s funny you say that. The boat came with a foil and trim tabs when I got it. First thing I did was rip them both off the boat because they severely affected the boats performance. Oddly enough the foil (even though seeming to be mounted properly and in great condition) would send the boat hard into a right bank when applying throttle! It would have me and anyone on the boat shaking in our water shoes!! Lol

 

[lvluck]

That boat needs to change some of the old parts, thorough the testing, and find the issues that slow your boat. check the#6 of the comment if that helps.

1995 Armada Marada 2100MVB "Executive Series" new to me boat QUESTIONS...

I purchased a boat, 1995 Armada Marada 2100 MVB "executive series", from the estate of a gentleman whom purchased the boat new. It was kept in a covered lift, out of the water, under a full cover and serviced by the local lake marina regularly. I am a big guy at 6'2" and 260lbs and checked the...

forums.iboats.com

 

[Seaduction19]

Hey y'all!!! So spring has arrived and I was able to take the boat out twice. The first day I went out on the river, I was with my buddy (160lbs man), little gear and about 5 gal. of gas. With the 5 blade high-five 19p prop on at WOT and completely trimmed out I was doing 38mph at 4600 rpm. This calculated to be about 17% slip. I then installed a Turning Point 3 blade 21p filled the tank with 24gal of gas so about 160lbs, added my girlfriend and some fishing gear. Opened the boat up again and at WOT all trimmed out I was getting 40mph at 4100 rpm which calculated to 11% slip. Its a little better.

 

[Bondo]

Ayuh,..... Welcome Aboard,..... You need abit less pitch, to get the rpms closer to 4800 rpms,....

 

[Scott06]

Try the same prop in a 19” pitch should put you about 4500 rpms

 

[Seaduction19]

I sent the new 21p back because I wasn't reaching the rpms I wanted. It had a 14 1/4in diameter. I don't really want to go lower than that pitch because the theoretical speed a 19p is supposed to create wouldn't fix the issue im trying to solve (I want to try and get the boat in the high 40's.) Im thinking about dropping the extra money on a name brand enertia 21p that has a 13.6in diameter to see if that helps not only raise rpm but also gets me a little faster than the 21p turning point express I had on it. What are your guys thoughts?