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New boat porposing when trimming up - what to do? Is trim useful for anything other than obstacle avoidance?
New 21' Larson I/O 5.0 L, porpoises at high speed with trim anything
other than full down trim. Why? What to do? I saw the post on hydrofoil and porpoising, someone suggested that removing the hydrofoil on his outdrive could make matters worse. How about the reverse, install a hydrofoil to improve matters? What's the downside? I am always skeptical about aftermarket devices like these because you would think that a manufacturer would ofer them standard or at least as an option if they meaningfully improved performance with little downside. According to the manufacturer, trim up improves speed and turning performance when on-plane. I have not been able to play around with this much because of the porpoising situation? Therefore, I pretty much raise the prop only to avoid obstacles at this time. Am I getting the point of trimming-up as far as boat performance? Mitch Gossman |
New boat porposing when trimming up - what to do? Is trim usefulfor anything other than obstacle avoidance?
Mitchell Gossman wrote:
New 21' Larson I/O 5.0 L, porpoises at high speed with trim anything other than full down trim. Why? What to do? I saw the post on hydrofoil and porpoising, someone suggested that removing the hydrofoil on his outdrive could make matters worse. How about the reverse, install a hydrofoil to improve matters? What's the downside? I am always skeptical about aftermarket devices like these because you would think that a manufacturer would ofer them standard or at least as an option if they meaningfully improved performance with little downside. According to the manufacturer, trim up improves speed and turning performance when on-plane. I have not been able to play around with this much because of the porpoising situation? Therefore, I pretty much raise the prop only to avoid obstacles at this time. Am I getting the point of trimming-up as far as boat performance? Mitch Gossman |
New boat porposing when trimming up - what to do? Is trim usefulfor anything other than obstacle avoidance?
Mitchell Gossman wrote:
New 21' Larson I/O 5.0 L, porpoises at high speed with trim anything other than full down trim. Why? What to do? I saw the post on hydrofoil and porpoising, someone suggested that removing the hydrofoil on his outdrive could make matters worse. How about the reverse, install a hydrofoil to improve matters? What's the downside? I am always skeptical about aftermarket devices like these because you would think that a manufacturer would ofer them standard or at least as an option if they meaningfully improved performance with little downside. According to the manufacturer, trim up improves speed and turning performance when on-plane. I have not been able to play around with this much because of the porpoising situation? Therefore, I pretty much raise the prop only to avoid obstacles at this time. Am I getting the point of trimming-up as far as boat performance? Mitch Gossman Do you happen to have trim tabs on that boat? |
New boat porposing when trimming up - what to do? Is trim useful for anything other than obstacle avoidance?
Far as I can tell, someone wrote:
install a hydrofoil to improve matters? What's the downside? I am always skeptical about aftermarket devices like these because you would think that a manufacturer would ofer them standard or at least as an option if they meaningfully improved performance with little downside. I thought the same thing for a good while. I used to ride a motorcycle back in the 80's. To improve comfort, I bought a "Windjammer" fairing, which was a windshield with "lowers" to protect the entire body from wind and rain. http://www.xs11.com/tips/modifications/wjv.jpg It worked very well. Only Harley (and maybe BMW) offered fairings. Even the famous Honda Goldwing did not have one available from Honda until years later. Now virtually ALL touring motorcycles come with fairings standard. Windjammer went out of business when motorcycles started making their own. |
New boat porposing when trimming up - what to do? Is trim useful for anything other than obstacle avoidance?
Hi Mitchell,
Is there any way to get more weight up forward in the boat? When you have you outdrive or outboard fully down tight to the transom and your boat still porpoises, I believe it is a weight transfer problem? Maybe when you have a load in the boat with more people, fuel and gear, it would be just fine and would take some trim without porpoising? -- Bill Kiene Kiene's Fly Shop Sacramento, CA, USA Web site: www.kiene.com "Mitchell Gossman" wrote in message om... New 21' Larson I/O 5.0 L, porpoises at high speed with trim anything other than full down trim. Why? What to do? I saw the post on hydrofoil and porpoising, someone suggested that removing the hydrofoil on his outdrive could make matters worse. How about the reverse, install a hydrofoil to improve matters? What's the downside? I am always skeptical about aftermarket devices like these because you would think that a manufacturer would ofer them standard or at least as an option if they meaningfully improved performance with little downside. According to the manufacturer, trim up improves speed and turning performance when on-plane. I have not been able to play around with this much because of the porpoising situation? Therefore, I pretty much raise the prop only to avoid obstacles at this time. Am I getting the point of trimming-up as far as boat performance? Mitch Gossman |
New boat porposing when trimming up - what to do? Is trim useful for anything other than obstacle avoidance?
I do not, what could they do for me and my modest vessel?
Harry Krause wrote in message ... Mitchell Gossman wrote: New 21' Larson I/O 5.0 L, porpoises at high speed with trim anything other than full down trim. Why? What to do? I saw the post on hydrofoil and porpoising, someone suggested that removing the hydrofoil on his outdrive could make matters worse. How about the reverse, install a hydrofoil to improve matters? What's the downside? I am always skeptical about aftermarket devices like these because you would think that a manufacturer would ofer them standard or at least as an option if they meaningfully improved performance with little downside. According to the manufacturer, trim up improves speed and turning performance when on-plane. I have not been able to play around with this much because of the porpoising situation? Therefore, I pretty much raise the prop only to avoid obstacles at this time. Am I getting the point of trimming-up as far as boat performance? Mitch Gossman Do you happen to have trim tabs on that boat? |
New boat porposing when trimming up - what to do? Is trim useful for anything other than obstacle avoidance?
I certainly agree with you. The needs of people vary so much so
manufacturers want to provide as standard equipment only the bare minimum rather than provide gold-plated features that may benefit only a few. For instance, a modest airplane does not require a fancy autopilot. BUT... A wing-shaped piece on the outdrive that could easily be molded into the rest of the outdrive or bolted on for a few bucks that can significantly improve performace and specs to brag about in shiny brochures? Why not? Far as I can tell, someone wrote: install a hydrofoil to improve matters? What's the downside? I am always skeptical about aftermarket devices like these because you would think that a manufacturer would ofer them standard or at least as an option if they meaningfully improved performance with little downside. I thought the same thing for a good while. I used to ride a motorcycle back in the 80's. To improve comfort, I bought a "Windjammer" fairing, which was a windshield with "lowers" to protect the entire body from wind and rain. http://www.xs11.com/tips/modifications/wjv.jpg It worked very well. Only Harley (and maybe BMW) offered fairings. Even the famous Honda Goldwing did not have one available from Honda until years later. Now virtually ALL touring motorcycles come with fairings standard. Windjammer went out of business when motorcycles started making their own. |
New boat porposing when trimming up - what to do? Is trim useful for anything other than obstacle avoidance?
"Mitchell Gossman" wrote in message
om... New 21' Larson I/O 5.0 L, porpoises at high speed with trim anything other than full down trim. Mitchell - first and easiest fix could be to put some weight forward. I would also recommend that you consider trim tabs - either fully adjustable tabs or "Smart Tabs" type. You can find a lot of discussions on both types on www.iboats.com forums - search on those two subjects for a lot of (what I think is) good info. Good luck and have fun with your new boat. Cam |
New boat porposing when trimming up - what to do? Is trim useful for anything other than obstacle avoidance?
1. What prop do you have. This is a heavy boat and it needs a good SS prop
w/ some bow lift in it to help hold the bow up when you start trimming. I would suggest a good SS 4 blade. 2. Trim angle is all about your speed, weight distribution, and conditions. As you increase speed - you should be able to trim out. If you are running wide open and bump the trim and the boat starts porpoising - there is a problem w/ either the prop or the hull or the weight is all forward. 3. For trim to work - you need less weight in the bow (not more as suggested). Move weight to the rear (especially a heavy cooler). 4. The hydrofoil will stop porpoise by pushing the bow down (same as leaving the trim down). It will not help w/ performance in terms of getting more boat out of the water which is the purpose of trim. 5. Trim tabs do the same thing bow allowing you to push the bow down more. Will not solve this problem. The are great for helping to plane and stay on plane at low speed. The also allow you to adjust side to side lean. Try a 4 blade SS prop. I think it will solve your problem. -- Tony my boats at http://t.thomas.home.mchsi.com "Mitchell Gossman" wrote in message om... New 21' Larson I/O 5.0 L, porpoises at high speed with trim anything other than full down trim. Why? What to do? I saw the post on hydrofoil and porpoising, someone suggested that removing the hydrofoil on his outdrive could make matters worse. How about the reverse, install a hydrofoil to improve matters? What's the downside? I am always skeptical about aftermarket devices like these because you would think that a manufacturer would ofer them standard or at least as an option if they meaningfully improved performance with little downside. According to the manufacturer, trim up improves speed and turning performance when on-plane. I have not been able to play around with this much because of the porpoising situation? Therefore, I pretty much raise the prop only to avoid obstacles at this time. Am I getting the point of trimming-up as far as boat performance? Mitch Gossman |
New boat porposing when trimming up - what to do? Is trim useful for anything other than obstacle avoidance?
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New boat porposing when trimming up - what to do? Is trim usefulfor anything other than obstacle avoidance?
Mitchell Gossman wrote:
New 21' Larson I/O 5.0 L, porpoises at high speed with trim anything other than full down trim. Why? What to do? I saw the post on hydrofoil and porpoising, someone suggested that removing the hydrofoil on his outdrive could make matters worse. How about the reverse, install a hydrofoil to improve matters? What's the downside? I am always skeptical about aftermarket devices like these because you would think that a manufacturer would ofer them standard or at least as an option if they meaningfully improved performance with little downside. According to the manufacturer, trim up improves speed and turning performance when on-plane. I have not been able to play around with this much because of the porpoising situation? Therefore, I pretty much raise the prop only to avoid obstacles at this time. Am I getting the point of trimming-up as far as boat performance? Mitch Gossman Two items come to mind - weight distribution and propellor surface area. Move weight forward to reduce porpoising. This will compromise top speed, though, if you are proped right. A 4-blade prop is one quick fix, but the right 3-blade will be fine too. The porpoising you describe is likely from the inability of the prop to hold the bow up while on plane - the power is fine from the engine but it has to be applied to the water from the prop. You have to increase the surface area of the prop by having larger blades or more blades - there are options either way, the best would be to try several different ones on a trial basis from a good prop shop. Rob |
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