Changing boat to increase HP

Discussion in 'Boat Design' started by RLP, Apr 14, 2018.

  1. RLP
    Joined: Apr 2018
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    RLP Junior Member

    I just came into possession of a 1992 14’ Lowe V-hull that has an aluminum bench seat at the front and back of the boat but the middle seat is split, where one side is a live well and the other is a storage box. The bottom frame of the boat is reinforced to support a plywood floor. The Lowe website is missing that years catalog in their archive on their website but the exact same boat model that I have does appear in the 1991 Sea Nymph catalog. That Catalog lists the model as a Muskie 14M Deluxe and states that the max HP that boat can handle is 25HP. In that same catalog, it lists a regular 14M which can handle up to a 35HP motor. From what I can tell, the only differences between the two models is that the regular 14M has a full aluminum bench in the middle instead of the split boxes and it does not have the reinforcement for a plywood floor.

    Screen Shot 2018-04-07 at 9.11.43 PM.png Screen Shot 2018-04-05 at 6.59.54 PM.png

    So here is what I’m wondering. If I were to swap the split seats for a full bench, would my boat be able to handle a 35HP? I hate to give up the free space but the 10 HP increase may be too good to pass up.
     
  2. RLP
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    RLP Junior Member

    So here's a picture of the reinforcement that holds up the flooring. IMG_0870.JPG
     
  3. Yellowjacket
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    Yellowjacket Senior Member

    It most likely has to do with the flotation required for the calculated motor weight. The USCG calculates a weight for the motor based on the hp rating and this may or may not be relevant since some 35 hp motors weigh the same as the 25 and the only difference is that the 25 motor has a smaller carb or is restricted in some other way. The seats have foam under them to provide flotation when swamped. That's a lot of floatation that is eliminated when you take the seat out. There is floatation foam under the floor, but there isn't nearly as much under there as there would be if you had a third seat.

    So long as you pick a 35 hp motor that is light then you are likely fine. If you want to you could cut additional foam sheets and lay them under the floorboards and that would likely be just as effective as adding the third seat.
     
  4. philSweet
    Joined: May 2008
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    philSweet Senior Member

    If you are planning to change the boat in this way, you need to do so in a way that meets the current requirements, not the ones from '92. And this may be an additional challenge since the weight allowance for design purposes has been increasing, and a new standard set of weights is going into effect this summer. The boat might only rate a 15hp now. There are a couple of other threads discussing the upcoming changes. USCG table of outboard motor weights for calculating flotation https://www.boatdesign.net/threads/uscg-table-of-outboard-motor-weights-for-calculating-flotation.57950/#post-804120

    Just to point out the obvious, the plate on the boat will still say 25 hp or whatever. You won't be able to register or operate the boat legally anywhere with a larger motor. To get the higher rating and a capacity plate, you would have to decommission the boat and re-register it as a home-built after the mods. How much of a pain that will be will depend on where you are at.
     
    Last edited: Apr 14, 2018
  5. messabout
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    Location: Lakeland Fl USA

    messabout Senior Member

    The 25 will propel the boat at a plenty fast rate. I would guess in the region of 30mph. Do you actually need to go faster than that in such a small boat? That boat will run in the low 20s with a 9.9 with two medium weight passengers and gear. Consider that that nice little boat is not now, and never was intended to be a speedster. It is a utility boat that does its' job well. Consider also that if you go faster you are likely to loosen some of your dentition because it will pound noisily and dynamically. If you need to pull water skiers, or tubers, the 25 will get the job done but perhaps not a tournament speeds.
     
  6. RLP
    Joined: Apr 2018
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    RLP Junior Member

    This boat will be used for fishing only, no water skiing. It takes about an hour to get to the good fishing spots, so the faster the better but yes, within reason. I’ll keep it at 25.

    Here’s another idea I had. I would really like to replace the bench seat in the back with two side boxes so that I could sit diagonal while steering. If I fill both boxes with styrofoam and fill the two middle boxes as well, that should be the equivalent amount of floatation as to what I have now. Will doing so cause any structural deficiencies though? I’d be happy to figure out the required floatation for todays standards but I can’t seem to find the info without having to buy the book.
     
  7. Yellowjacket
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    Yellowjacket Senior Member

    Nonsense... boats are running with motors exceeding the plate ratings all over the USA.... The ratings are based on the Coast Guard formula and this is based on an arbitrary formula that relates horsepower length and transom width... Here is a clip from the Whaler forum that talks about the subject...

    Is powering above the rated maximum legal?

    The United States Coast Guard has an opinion on this frequently asked question, and their answer [which at one time was on their] website [but due to continual re-design of their website seems to have moved somewhere that I cannot find anymore] is reproduced below:

    Can I use a bigger motor on my boat than what it's rated for?

    There are no Coast Guard regulations against exceeding the safe loading capacity, or power ratings, however, there may be State regulations or restrictions from your insurance company which prohibit this. There is a Coast Guard regulation that gives Coast Guard Boarding Officers the power to terminate the use of a boat (send it back to shore) if, in the judgment of the Boarding Officer, the boat is overloaded. There is no fine for this, unless the operator refuses the Boarding Officer's order. We certainly hope that you will abide by the rating, as overloading may lead to capsizing or swamping of the boat. NOTE: The Coast Guard Capacity Information label is required only on monohull boats less than 20' in length. The label is not required on multi-hull boats, pontoon boats (catamarans), or on any sailboats, canoes, kayaks, or inflatable boats, regardless of length.

    As the Coast Guard mentions, local regulations may apply. For example Alabama law says that powering a boat above the
    Capacity Plates
    (ORC 1547.39 & ORC 1547-40)


    No person shall operate or permit operation of a watercraft in excess of any of the stated limits on the capacity plate. When no capacity plate exists, no person shall operate or permit operation of a watercraft if a reasonably prudent person would believe the total load aboard or the total horsepower of any motor or engine presents a risk of physical harm to persons or property.

    To help locate applicable law in your jurisdiction, you may find the website of the National Association of State Boating Law Agencies to be helpful. They provide a guide to state boating regulations.

    It should be noted that in some cases there are pamphlets or guidelines issued by state regulatory agencies that contain recommended practices which may propose higher standards than those actually contained in the state law.

    Will dealers or service shops install an engine that exceeds the maximum rated horsepower for a boat?
    It is not unusual for a dealer to decline to install an outboard motor on a boat where the motor exceeds the horsepower shown on the rating plate. This seems to be fairly common practice, particularly if the dealer is also selling the boat. On the other hand, it does not seem to be particularly difficult to locate a service shop or facility that will install a motor which exceeds the rating plate horsepower. Most states do not appear to license the profession of installing outboard motors, so there does not seem to be any particular regulatory difficulty in performing this service. Many dealers who decline may cite risks of liability, but in most cases they already have insured themselves against such liabilities and claims. Separating the sale of the motor from the installation of the motor seems to make it easier to find a dealer or service shop willing to make such installations.

    Can insurance coverage be purchased for boats powered above their rating?
    Boats equipped with engines whose horsepower is above that shown on their rating plate can be insured, but often at greater cost than for the same boat with engines conforming to the horsepower limitation. It may be necessary to change insurance companies, as some will decline. At this writing it is known that the Traveller's Insurance Company will write policies covering boats with engines that exceed the rated horsepower, although they do charge more than for the same boat with engines conforming to the horsepower limitation. It is important to disclose the horsepower of your engine(s). Usually an insurance policy will contain the serial number of the specific engine being covered and its horsepower. Misrepresentation of the engine horsepower would be a fraud and could result in lack of coverage. Some insurance companies raise the cost of insurance in proportion to the boat's maximum speed.

    Bottom line is that putting a 35 on a 14 foot boat and maybe doing 30 mph instead 0f 25 isn't going to be an issue and nobody is going to make this an issue when there are 14 foot boats running around with 75 hp motor and doing 80 mph all day long... As noted above the rating wasn't because of excessive speed or stability concerns, it was most likely due to the limited floatation and if you increased the floatation by adding foam under the flooring that will likely be just fine.
     
  8. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    It's pretty easy to figure out how much your boat can take in regard to HP. Provide the width of the transom at it's widest spot and the length of the boat and I can offer the ranges. You transom reinforcement may need some additions for the 35 HP, but this is easy.

    The hull you have will scoot right along in the high 20's with little trouble. This is the ideal cruising speed of a boat shaped the way yours is. If you add the 35 HP, you'll push above 30 and the ride will change considerably. Simply put, you can gain a few MPH on the top end, but you'll likely find you're throttling down a little to keep the boat from hammering your fillings out. This boat shape is intended for mid to upper 20's and if pushed over this, she'll pound pretty good.
     
  9. RLP
    Joined: Apr 2018
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    RLP Junior Member

    The boat is 14’-5” long. The transom is 5’ wide and 16” tall.
     
  10. gonzo
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    gonzo Senior Member

    There is a 58 lb difference between the boats. The deluxe model is heavier even though it has a smaller center seat. I would think that the extra weight is most likely into reinforcements to account for more HP
     
  11. ondarvr
    Joined: Dec 2005
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    Location: Monroe WA

    ondarvr Senior Member

    Yellow jacket

    It's nice to see someone reads the actual rules and passes on the real statement by the CG. On other sites this comes up very often and people think there's a federal law in place, or that you can't insure the boat.

    I did the research and went to several insurance companies and asked them about it. None turned me down, some didn't even care, others said the premium would be slightly higher.

    The CG can't do anything unless you operate the boat in an unsafe fashion.

    "Just to point out the obvious, the plate on the boat will still say 25 hp or whatever. You won't be able to register or operate the boat legally anywhere with a larger motor. To get the higher rating and a capacity plate, you would have to decommission the boat and re-register it as a home-built after the mods. How much of a pain that will be will depend on where you are at."


    "Nonsense... boats are running with motors exceeding the plate ratings all over the USA.... The ratings are based on the Coast Guard formula and this is based on an arbitrary formula that relates horsepower length and transom width... Here is a clip from the Whaler forum that talks about the subject..."
     
  12. RLP
    Joined: Apr 2018
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    Location: Nashville TN

    RLP Junior Member

    Gonzo, I think you have it backwards. The 14M Deluxe with the split center seats is heavier with a lower max HP than the 58 lb lighter 14M with a center bench seat. The extra 58 lb's in the deluxe is most likely due to the plywood floor which the regular 14m is missing.

    At this point I am fine with the 25HP limit but I would still like to hear if anyone sees any problems with my idea of replacing the rear bench seat with split boxes.
     
  13. gonzo
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    gonzo Senior Member

    Oops, so I got it backwards.
     

  14. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Those dimensions would permit a 50 HP outboard, though to be reasonable, this should be 40 HP as a max. With a 35 HP engine and about 1,000 lbs. of load, she'd run in the mid 30's which on this hull shape would be fast, but uncomfortable, (she'd pound pretty good). If the engine was sized down to say a 25 HP, with the same load, she'd be high 20's maybe low 30's, which is more comfortable for this type of hull.
     
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