Propping my boat to stay on plain

[Searay176]

I am sure this question has been ask a thousand times before..... But I have a 2002 Sea Ray 176br with a Merc 3.0 with an Alpha One outdrive, 130hp..... My goal is to be able to get on plain quickly and then stay there at lower speeds... Most of out boating is done in the rivers of SE Louisiana were speed is not something of an issue and the kids often kneeboard or tube. The boat has the stock prop on it... A 14.25 X 21 I believe. WOT is 4800 at about 40ish mph. There is usually two adults and 3-4 kids in boat with a cooler and snacks... Can some one tell me if this is a prop issue or a trim tab issue?

Regards,

Jeff

 

[cribber]

Re: Propping my boat to stay on plain

I have a similar setup and put a SS 20" pitch 4 blade on it and gained a second for my holeshot and about one MPH lower plane speed. I gave up about 8 mph for my WOT speed when I swapped out my props. I went with a Stilleto Bay Pro II. Play with a prop calculator to see what different options will gain you.

 

[John_S]

Re: Propping my boat to stay on plain

I am sure this question has been ask a thousand times before..... But I have a 2002 Sea Ray 176br with a Merc 3.0 with an Alpha One outdrive, 130hp..... My goal is to be able to get on plain quickly and then stay there at lower speeds... Most of out boating is done in the rivers of SE Louisiana were speed is not something of an issue and the kids often kneeboard or tube. The boat has the stock prop on it... A 14.25 X 21 I believe. WOT is 4800 at about 40ish mph. There is usually two adults and 3-4 kids in boat with a cooler and snacks... Can some one tell me if this is a prop issue or a trim tab issue?

Regards,

Jeff

Welcome to iBoats.

If those numbers are with your normal load, you are at the upper end of your wot range. I'd look into smart tabs to improve your planing. Do a search on "smart tabs" and you will have more than enough reading. Key is your transom and having the appropriate area to mount them. After that, if you need some extra pulling power, you could drop down an inch or two of pitch, and possibly go to a 4 blade.

 

[steelespike]

Re: Propping my boat to stay on plain

Tabs both active and passive can be very effective,improving hole shot and keeping on plane at reduced power, improve ride, reduce no wake speed wander.
I hasitate to put holes in a boat below the water line and active tabs do add some complication to the boat and tabs do use ever so slightly more fuel unless fully retracted.
Hard to measure the difference.
A 4 blade will get you up quicker,and stay on plane at lower throttle with less fiddling.
It may also slightly improve ride and handle better at the dock. Usually there is a slight loss of speed but I have seen some that maintained speed and actually gain speed but it is the exception.It is usually suggested to drop one inch in pitch going to a 4 blade.

 

[John_S]

Re: Propping my boat to stay on plain

Tabs both active and passive can be very effective,improving hole shot and keeping on plane at reduced power, improve ride, reduce no wake speed wander.
I hasitate to put holes in a boat below the water line and active tabs do add some complication to the boat and tabs do use ever so slightly more fuel unless fully retracted.
Hard to measure the difference.
A 4 blade will get you up quicker,and stay on plane at lower throttle with less fiddling.
It may also slightly improve ride and handle better at the dock. Usually there is a slight loss of speed but I have seen some that maintained speed and actually gain speed but it is the exception.It is usually suggested to drop one inch in pitch going to a 4 blade.

Just to clarify some on the tabs. Smart Tabs are passive. You adjust and test them after install, then forget about them. Manually controlled tabs, work like your trim adjustment, you adjust each side manually. These are active tabs.

IMO, active tabs are for big water, large wave type boating. You can adjust to multiple conditions. I wouldn't recommend them on a 17' bowrider running mainly on a river.

As far as hole below waterline, to me that is mainly a phych thing. After the first one, you realize that its not that bad. Be it tabs, transducer, swim platform, etc, eventually you will put a hole below the waterline. Like most things, do it it right with the right materials, and it won't be an issue.

Never thought about the gas milage before. Not sure if that applies to the smart tabs (outside of pre-planning speeds), but see if you left the active tabs down after being on plane, it would cause more drag, and lower milage slightly. I would think any prop that lowers wot speed also has impact on gas milage. I am not sure which has more impact? I've never really worried about gas milage pulling tubers, etc. Its going to be bad no matter what, and you don't want to think about it to detract from everyones fun!

 

[steelespike]

Re: Propping my boat to stay on plain

We need to keep in mind that a given motor will use the same amount of fuel at wot per hour regardless if it pushes a house boat or a speed boat.Its the speed reached that determines mpg. A motors gph(gallons per hour)at wot(wide open throttle) is about 10% of its rated hp.
a 100 hp uses about 10 gph.
Low to mid range performance is the 4 blades forte'
The 4 blade inproves hole shot a slight savings,stays on plane at reduced throttle
probably a savings, The right cruising speed it may excel.
But usually wot is the weak point of the 4 blade.
I think you would need a flow meter to tell the difference with the prop or tabs.

 

[Searay176]

Re: Propping my boat to stay on plain

Thanks for all the good information guys!!! So what I am hearing is if I have a 14.25X21 3 blade prop, go with a 14.25X20 4 blade SS?? I don't have an issue adding trim tabs if it will accomplish my goal.... As for gas mileage ...... If I were on a budget, I wouldn't have a boat.... Lol. Correct me if I am wrong, but if I have active trim tabs, then I could correct the boat angle side to side when cruzin right? Some times the kids all want to sit on one side of the boat and,.... Well you with kids know......

 

[John_S]

Re: Propping my boat to stay on plain

Thanks for all the good information guys!!! So what I am hearing is if I have a 14.25X21 3 blade prop, go with a 14.25X20 4 blade SS?? I don't have an issue adding trim tabs if it will accomplish my goal.... As for gas mileage ...... If I were on a budget, I wouldn't have a boat.... Lol. Correct me if I am wrong, but if I have active trim tabs, then I could correct the boat angle side to side when cruzin right? Some times the kids all want to sit on one side of the boat and,.... Well you with kids know......

While manual trim tabs could help compensate for variable loads, such as all the kids on one side, etc, using them all the time on a runabout, kneeboarding, tubing, etc, I believe will turn into a PITA.

As the captain of the boat, kids and adults, must know where they are suppose to sit, and no quick moving around while up on plane. If they don't want to listen, keep in at a slow, off plane speed, and no water sports. They seem to get it after that.

Going to ss on the four blade, may mean dropping another inch of pitch. That may be brand/model spcific, and would want input on the particular prop you are considering.

 

[John_S]

Re: Propping my boat to stay on plain

We need to keep in mind that a given motor will use the same amount of fuel at wot per hour regardless if it pushes a house boat or a speed boat.Its the speed reached that determines mpg. A motors gph(gallons per hour)at wot(wide open throttle) is about 10% of its rated hp.
a 100 hp uses about 10 gph.
Low to mid range performance is the 4 blades forte'
The 4 blade inproves hole shot a slight savings,stays on plane at reduced throttle
probably a savings, The right cruising speed it may excel.
But usually wot is the weak point of the 4 blade.
I think you would need a flow meter to tell the difference with the prop or tabs.

While I have seen a number of MPG "Sideway S curves" with a given boat/motor/prop combo, I can't say I've seen ones comparing 3 and 4 blade props. My guess would have been that there would be slightly different rpm range where each was the most efficient. It would be interesting to see the differences in magnitude at the most efficient spots. Can't say I've seen the with/without smart tabs MPG testing results either.

 

[Texasmark]

Re: Propping my boat to stay on plain

Lot of info thrown at you. More blades and less pitch mean more control at lower speed with heavier loads....simple as that. Anything that you can add beyond the transom will help give the boat transom lift which means planing out at lower speeds with less hp..less hp for a given engine means lower rpm's.....less hp means better fuel economy. Best fuel economy is just on plane where the bow just lays down...many boat performance curves on the www showing the efficiency at that point.

Mark