HP Ratings - Also Consider Weight

Discussion in 'Boat Safety' started by sgt_rob, Apr 19, 2006.

  1. sgt_rob

    sgt_rob Member

    Messages:
    961
    State:
    Bossier City, LA
    First of all, this is my opinion and only stems from my personal experience...

    It seems to me that back in the day of a "2-stroke only" boat motor world, weight was not a factor so the industry (or Coast Guard) came up with a calculation to figure how much power a boat could safely handle without having to consider the weight of the motor. I know there are also maximun weight capacities for a boat but I'm sure that weight is supposed to be evenly distributed and not hanging off your transom.

    When I went from a 2-stroke 20 HP (that was easily carried with one hand) to a 4-stroke 25 HP (150 lbs that is a strain no matter how I handle it) my transom gained weight and cracked as a result. Now that the transom has been rebuilt (and raised) I still have the weight to deal with which of course makes the transom sit low in the water. I was told last week that a Tahatsu 30 HP 4-stroke weights 200 lbs. Now I'm not sure on the rating for my boat because there isn't a tag on it but I would be willing to bet that it is rated for at least 30 HP. Knowing what a 150 lb motor does to it, I'd be a fool to strap a 200 lb motor on it no matter the HP rating.

    Do you think a dealer will tell you this stuff? I doubt it. When I bought my motor I asked the dealer if they normally put a motor that big on a 14' boat and he said "all the time". It's all about the bottom line, the mighty dollar and them hanging on what that little label on your boat says the Maximum Horse Power rating is.

    I believe that there should be an upgrade to the Maximun Horse Power ratings to include Maximum Motor Weight.
     
  2. Bobpaul

    Bobpaul New Member

    Messages:
    3,039
    State:
    Supply NC
    Your absolutely right Rob. Boats are built to accept a certain amount of forward force produced by the hp of the engine.

    The motor weight plays a big part when trailering the boat and the damage to the transom.

    Lighter motors should be tied down to eliminate the bounce and heavier motors need to be supported to eliminate the levering effect against the transom.
     

  3. copycat

    copycat New Member

    Messages:
    1,841
    State:
    New Jersey
    Rob, that is a really good point. I was not aware of the weight difference between 2 and 4 stroke outboards. I have a 14 foot jon that I use a 9.9 2 stroke on it and have thought about getting a 4 stroke for it in the future.
     
  4. jim

    jim New Member

    Messages:
    2,579
    State:
    Jacksonville NC
    Rob good point.I will say however that it is pretty much common knowledge that the 4 stroke engines weigh more than two stroke for various reasons.My boat is rated for 200hp and I have a Mercury Optimax on it now.The transom is rated for 550lbs however.THe New Verado I want weighs more than 550 so I can't get it.I have talked to the manufacturer and they are reinforcing transoms in the new model to support the heavier 4 bangers but that doesn't help me.On a similiar note I just read in a boating magazine that the weight capacities for boats were calculated back in the 60s when the average adult weighed 148lbs.Current average is 174 if I remember right.So if you have a data plate that says Max Cap is 5 adults they meant 740lbs NOT 870lbs.Go with the numerical weigh if listed.5, 210lb people will definitely lower your;) :p :) transom and reduce performance.
     
  5. tmuenster

    tmuenster New Member

    Messages:
    53
    State:
    South Dakota
    This is an excellent topic. Rob, you are right on track with the weight being a critical design consideration. I have discussed this topic with some marine engineers who design boats. Most new boats do have a spec for max engine weight. The consensus is that you should not put excess weight on the transom. There is a factor of safety in their calculations and I would feel comfortable with a small overage of less than 10% of the rated weight depending on the other items stored in the transom area (ie- battery, fuel, etc). The more of these items you can move forward, the more confident I would be in using the max weight size of an engine.

    Another consideration is using a setback bracket or jack plate. This weight should also be considered in the total engine weight. If you are using an extreme setback bracket it will also affect the center of gravity of the boat. The setback with act like a moment arm and add additional stress to the transom. Most large setback brackets have positive flotation to counter this force.

    The larger the motor, in terms of weight and hp, the more caution should be used when altering a boat from the manufacturers design. A 90 hp outboard will do a whole lot more damage if something goes wrong than a 10 hp kicker.

    Great post Rob!
     
  6. peewee williams

    peewee williams New Member

    Messages:
    3,111
    State:
    Pembroke,Georgia
    Your transom should be inspected before each use,yet is forgotten more often than the plug.High H.P.motors can exert a lot of force on a transom,when someone "pours the coal" to a large heavy,stationary boat.Also when you hit a object at high speed.The sight and sound of pieces of a large outboard cartwheeling through the air is awesome.It has the power to make a grown man cry.For sure if he is the owner.I once had my transom broke top to bottom in a freak accident with a gator,while running with a 8 h,p.motor on a 14 ft.aluminum John Boat.The Okefenokee swamp was very low due to drought,and the large gators were concentrated in the lake,eating the smaller ones(7 ft. and under).BAD place to sink.Bad things happen when least expected and at the worst times.peewee-williams
     
  7. Mr.T

    Mr.T Active Member

    Messages:
    2,554
    State:
    MO
    I think this business about 4-stroke engines being so much heavier than 2-strokes is mostly just a myth. Sure, they're a bit heavier but not really enough to matter, at least on the smaller engines.

    A Yamaha 2-stroke 115hp engine weighs 358 lbs; the 4-stroke 115 weighs 402 lbs, a difference of just 44 lbs. The Yamaha 2-stroke 50hp engine weighs 189 lbs; the 4-stroke 50hp weighs 237 lbs, a difference of 48 lbs. And in the small engines, a 9.9hp 4-stroke weighs 99 lbs; the 2-stroke 9.9hp weighs 79 lbs.

    Mercury's 4-stroke 115 hp EFI engine weighs in at 386 while their 115hp Optimax 2-stroke is 375 lbs -- only 11 lbs different. According to the Mercury web site, the 75hp engines weigh exactly the same as the 115hp engines, which I suspect might be inaccurate information on their part.

    If 50 lbs of engine weight means the difference between your transom cracking and not cracking, you've got bigger problems than worrying about whether you should run a 2 stroke or 4 stroke.
     
  8. lonegunman88240

    lonegunman88240 New Member

    Messages:
    61
    State:
    new mexico
    i got a 1970 alumacraft the coastguard sticker does give total weight, mine says 3 persons or 430lbs, then below it it says 650lbs total weight with motor and gear and persons
     
  9. ka_c4_boom

    ka_c4_boom New Member

    Messages:
    2,252
    State:
    Bedford,Ky
    i have a 40 hp mariner on a 16'72" com. river jon alumincraft both 1983 models but my transom has been reinforced on both sides with 20" of aluminum angle welded along top rail never noticed transom giving either way ; and have watched when on the water but iv also never run forward with the motor in the lock position i only lock down in reverse it also helps that i try not too take off real fast altho it would probly pull up a skier i prefer not to try its not a pleasure boat its for fishing if most people watch what they're doing they wouldnt end up in an embarrasing moment ,if i looked up and seen motor parts flying thruogh the air id cry too lol good luck and be safe guys
     
  10. JAYNC

    JAYNC Active Member

    Messages:
    1,312
    State:
    Newport N.C.
    Its accurate on the Mercury website, the 75,90,and 115 are the same exact block...(ALL FROM YAMAHA) The 75 and the 90 are exactly the same engine but jetted differently, on the 2005 models, or programed differently with the fuel injected model, I mean the same exact bore and stroke, only difference being rpm. The 115 is the same block but has a little bit different bore and stroke. I found this out after I bought my 75hp, but I am glad I did since my boat is fast enough with it.
     
  11. sgt_rob

    sgt_rob Member

    Messages:
    961
    State:
    Bossier City, LA
    You might have changed your mine if you had been in the middle of the river with me, the 25 4-stroke and the old transom. It was scary!!! Snap, Crackle and Pop were only three of the sounds it wade when I took off. Now it is solid; it has no noise but it still rides lower than I like due to the weight. Mine isn't the only boat around with that motor. A buddy of mine had a boat that rode lower than mine. So, while we value all opinions here in the BOC, you had to experience this one to understand just how bad it was before the transom modification. I'm not knocking 4-strokes but it is a fact that they are heavier. You ought to think twice before putting a 4-stroke on a small boat.
     
  12. AwShucks

    AwShucks New Member

    Messages:
    4,532
    State:
    Guthrie, Oklaho
    No matter as to what size motor your running, if your flirting with the max weight recommendation of a boat, you probably won't be around much longer. Don't count on their built in safety factor - as that was proably when the boat was brand new and most of our boats are no way near new. I offer some unasked for counseling to a friend of mine who practically overloads his boat everytime he goes out. He is not concerned because he believes it is under the max weight rating. To top it all off, all the life jackets and floating cushings are in lockers where they wouldn't even float if the boat sank. tsk, tsk, tsk. Keep telling him I'm going to have to take time off from fishing just to go to his funeral, but it don't register in his mind as to what I'm saying.
     
  13. loanwizard

    loanwizard Well-Known Member

    Messages:
    3,297
    State:
    Coshocton,
    I have a 1987 Landau 1654 modified jon boat with a 40 hp jet (25 approx) I was looking for a tag the other day. I am thinking about putting a 90 Mariner on it but don't know if it is too big. It probably is but it is just a thought.
     
  14. BoG

    BoG Member

    Messages:
    46
    State:
    Delaware
    Name:
    Bo
    One of my favorite books is the "Outboard Boaters Handbook". The author is very big on not going to the max hp. I have owned quite a few boats over the years, and not once have I gone to the max on hp, and not once have I been disappointed. My current boat is rated for a 150, and I chose the 135. Why? Only 2 to 3 more mph and uses more gas. It's a two stroke not a four, but why would anyone want to go faster and spend more on gas unless big bucks are on the line like BASS guys.

    Boating and fishing should be enjoyed. The scenery that goes by in a blurr is not nearly as interesting.

    Just my 2 cents.

    Bo
     
  15. rcneman

    rcneman New Member

    Messages:
    482
    State:
    TN
    Dang man...i see 16ft boats goin down the freeway with 225 HP evinrudes...22 footers with 250 HP Johnson's.....come the frick on!


    Peeps want SO many horses on the back of the boat...then we hear about how 6 people died at 5 am hittin a log in the lake.

    When will it end? How many peeps have to die? How fast do you REALLY need to get to your fishin hole?? GET a grip people!

    hope your right with the Maker!
    rc
     
  16. Mark J

    Mark J New Member

    Messages:
    9,407
    State:
    Four Oaks, NC
    Robert, many hull designs are ineffecient at low or even medium speeds. One of those is the bass boat hull.
    Others consist of the deep V variety.
    It takes alot of horses to get a deep V on plane.

    Thats why you may see a 250 horse on a 20 foot deep V fishing boat and a 75 horse on a 21 foot flat bottomed skiff. Flat bottoms are an efficient hull design for low speed. So are displacement hulls.

    There will always be hull designs that are inefficient and there will always be big engines, along with fast boats.
    you cant have both worlds in one design and it be efficient in either one.

    There is a demand for them.

    So the next 225 or 300 you see bolted to a transom, it may be required to get the boat up on the running pad. Once on the pad you got some play in the throttle along with play in the speed.

    I myself am more into efficient hull designs with the rising cost of fuel.
    I'm also into alternative methods of modern day boat building that creates lighter and stronger hulls.
    These methods are being used from canoes to super yachts but you wont find them at your local boat dealership. Paying some poor sap 8 bucks an hour to run a chopper gun is alot cheaper and makes alot bigger profit margins then paying craftsmen a fair wage to build a boat with efficiency in mind..
     
  17. janton311

    janton311 New Member

    Messages:
    654
    State:
    Wichita Kansas
    I've got a 14' flat bottom. shes sporting a minn kota 35 lb. thrust trolling motor. Light weight, good gas mileage. I like it...:lol:
     
  18. tmuenster

    tmuenster New Member

    Messages:
    53
    State:
    South Dakota
    Well said Mark. Boat design is a difficult set of compromises. I have a 200 hp jet on a flat bottomed RiverPro. The boat does what is it designed to do very well. I also have a Zodiac F470, a military surplus inflatable assault boat, with a 25 hp Yamaha two stroke that will do almost 25 mph and get very good fuel economy.

    Mark, I tried to give you rep points for you post but I guess I need to spread them around a bit more. You know a lot about boats and I always enjoy reading your posts. Thanks

    Tom